A Very Lightweight, Fuel-efficient, No Fuss, No Fumbling Alcohol Stove System
Introduction: Filling a Lambda Stove Using the Snuffle Flask
The Lambda stove is my personal MYOG Alcohol Stove that I plan on writing a future article about. This article will cover the Snuffle Flask an alcohol fuel dispenser than can be used with any alcohol stove. A fuel efficient cooking system consists of a stove, the environment, one’s fuel supply, the ability to measure, a lighter/starter, a pot, a pot stand, and a windshield. Each item has to work together properly to create an efficient system.
The Snuffle Flask is a fuel bottle with an integrated fuel measuring and dispensing system. It is a simple and reliable way to fill the exact amount of alcohol needed for any alcohol stove without utilizing multiple devices.
This project is not a beginner’s project. You will be working with very sharp tools. Be sure you have the necessary experience to work safely with the tools you will be using. And: alcohol fuel burns. Use common sense and don’t burn yourself or anything else.
Measuring fuel without the Snuffle Flask
Everyone who has operated alcohol stoves knows that accurately measuring the amount of alcohol going in the stove is challenging. You are supposed to use a small measuring cup, but if you are tired and hungry, filling the necessary amount of alcohol into the cup is difficult. Trying to get a decent read on the amount of alcohol poured when it’s dark is difficult also. It is difficult to fill the stove without spilling, to keep track of the fuel bottle cap, and to keep the fuel bottle from tipping over. After all, you are in the backcountry, far from any picnic table. Also, dexterity and intellectual abilities tend to deteriorate rapidly once a person gets tired and hungry.
The video clips on youtube make operating an alcohol stove look easy. Alcohol stoves can be quite sensitive to their environment. The usual “penny stove” will die in anything but warm and sunny conditions. I have once used nearly 10.1 oz. (300ml) of alcohol to cook 33.8 oz. (1 liter) of soup. I missed a warm meal once because of this. Here is my solution to provide a no fuss, no fumble, no spilling, and easy to operate system that works under most conditions encountered on backpacking trips. The system described can even be operated wearing gloves.
The core element of the system is the fuel bottle. For one to two person use, a fuel bottle of 8.5 oz. (250ml) to 11.8 oz. (350ml) is fine (for me) and will work for a couple of meals. Actually, one single 11.8 oz. (350ml) bottle of fuel (yellow “Heet”) was more than plenty for a 5-day/4-night summer trip my wife and I took in the Sierra Nevada. We were at 10’000 ft+ (3048 m+) elevation and had dried meals to rehydrate and no restrictions on the amount of tea, coffee, soup, etc. For 2 to 3 people or for longer trips, I may take a 16.9 oz. (500ml) bottle, or I may prefer to refill my smaller bottle every once in a while. Larger groups will carry more than one system, especially when will have to melt snow to get their water.
The diameter of the bottle cap matters when wearing gloves. There are mainly three sizes of bottle cap diameters on the most popular PET bottles. Water or pop/soda bottles usually come with cap diameters of 1.1 in. (29mm) or 1.3 in. (32mm). You will also find the lightest bottles in this group. You might feel they are a bit on the flimsy side for a fuel bottle. I believe, however, that they are okay as I integrate them into my system and carry them in my backpack, protected by the windshield and another (flimsy) PET-container. Lightweight gear is designed for use, not for abuse. If you want to abuse your gear, go to the army surplus store. The bottles containing fruit juices and smoothies come with 1.6 in. (40mm) caps and tend to be a bit sturdier. The 1.6 in. (40mm) caps are nice to operate with your gloves on, too.
Developing the Fueling System: The Stages of Error
- The usual measuring cup. There is no easy read of the amount measured.
- This was my system during the 2015 season. It consisted of a 10ml syringe fitted with a short length of flexible fuel tubing from the RC model hobby shop. It is easy to read, but the fuel cap has to be taken off and left unattended during operation. The flexible tubing can direct the alcohol into the wrong compartment of the stove if you are using a Trail Designs 10-12 stove, for example. A piece of stiff tubing is a wiser choice.
- This model is an air freshener pump with a drilled out nozzle fitted to your fuel bottle. Needs two hundred (sic!) pump strokes to get out .7 oz. (20ml) of alcohol. Not trail worthy!
- This was my first attempt with a built-in .2 oz. (5ml) syringe and also with two valves from a foot freshener spray. A real pump puts out .2 oz. (5ml) of alcohol on each stroke. Aptly called the “Snuffle Flask” by my elder son, the flask needs an air bleed device to let in some air, so there are three holes in your bottle cap. The holes pose sealing issues. The two caps used as an air bleeding device and fuel spout are prone to leakage, too.
- The photo shows the enhanced Snuffle Flask with an air bleed screw and larger diameter bottle cap to accept a 10ml syringe. Handling all three devices on the cap at the same time is still a bit fiddly (open air bleed screw, uncap fuel outlet, pump the necessary amount, close all openings again). At least, there are no items of which to keep track. Everything is attached to the fuel bottle. There are still three holes in the bottle cap that are prone to leakage. The air bleed is a screw that is a bit tricky to manufacture. During a family discussion, I proposed to skip the air bleed screw and replace its function by merely untightening the bottle cap. Whereupon, my elder son proposed to leave out everything except the syringe mounted to the cap – bingo!
- This photo depicts the first versions of the final design of Snuffle Flask. Leakage remained a problem, as gluing a syringe to a bottle cap is problematic, i.e. the soapy type of plastic used for bottle caps tends to split from any type glue.
- This is the first coupling-nut system. This system presses everything down on a sealing ring. It is fuel tight and trail-worthy.
- Same as #6.
Fuel Bottle Design and Construction of the Snuffle Flask
I will show you three fuel bottles:
- The “Simple-simple Flask” may leak unless you are proficient with hot glue or find a lucky combination of a syringe and bottle cap (see pics 02, 45 and 46);
- The “Screw-on cap Flask” is the “normal” choice for anyone. It uses a wide cap (see pic 51, the right flask); and
- The “Coupling-nut Flask,” is probably the safest example, but a bit tricky to make (see pics 51, left flask, and pic 65). Choose a bottle with a large cap if you intend to operate it wearing gloves.
Materials Required for All Three Bottles
- This construction requires a wide-mouthed, clear PET bottle, preferably with 1.6 in. (40mm) or 1.3 in. (32mm) outer cap diameter, 8.5 oz. (250ml) to 11.8 oz. (350ml). I do not like colored bottles; I want to see what’s happening inside. Get a couple of different drinks, smoothies and the like; drink them, clean the bottles, and have a close look at their cap. The caps have an inner rim to fit the inside of the bottleneck. Keep off bottles without this, like the ones with an additional sealing foil on the mouth when you take off the cap. These caps will not make a reliably tight seal. Have several caps on hand because you may not succeed with your first cuts into the cap.
- You’ll need 20ml or 10ml disposable syringes without needles. Get half a dozen; both sizes are very reasonably priced at your drugstore. Don’t expect your first try to be entirely successful. The 10ml requires more pumping on the trail while the 20ml is a harder fit but more convenient to use.
- You’ll also want silicone rubber cement. I use a heat resistant glue which I can also use on my stoves. The shelf life of this sealant is limited.
- Hot glue sticks.
- Two little self-tapping screws about 13/64 in. (5mm) long, about 5/64 in. (2mm) outer diameter, 5/34 in. (4mm) head width, or, two equally small metal screws with nuts. If you can fit a 10ml syringe, you may get away with slightly larger screws.
- A short end of plastic tubing measuring about 5/64 in. (2mm) to 1/8 in. (3mm) in diameter (derived from an old air freshener bottle, for example, any other pump-spray, or clear pushrod housing from the RC-model hobby shop).
- X-Acto type knife with a few pointed blades (#1 on pic)
- Hot glue pistol (glue gun) with glue sticks
- Razor saw, small hacksaw or Dremel type table saw
- Circular cutter. In order to make a cutter (#2 on pic) yourself you will need:
- A small hardwood block 1 1/32 in. x 19/32 in. x 25/64 in. (50mm x 15mm x 10mm, roughly)
- An X-Acto type blade
- Three small self-tapping screws
- One sturdy pin of .1 in. (1.5mm) diameter (the circular cutters available in the handicraft section of your department store or hardware store tend to be too flimsy to do our job)
- Hand drill or drill press with .1 in. (1.5mm) and .1 in. (2mm) bits (#3 on pic.)
- Small metal ruler 7.9 in. (200mm) long. The one shown is flexible and has a thickness of exactly .02 in. (0.4mm); #4 on pic
- A sliding caliper is an asset, but this is a pricey precision tool (keep your hands off cheapos, they are not accurate enough – buying cheap means buying twice!)
- 220 grit sandpaper
- Sharpie type pen
- Round awl or prick
- Candle or lighter
- Medium sized half round file
- Small half round file (“needle-file” type)
- Standard pliers
- Small wire cutter
Measure the diameter of your syringe (a caliper comes in handy). Wrap a strip of paper around your syringe and mark where the rest of the strip reaches its beginning. Make sure the strip is wound tightly. Using a pen to mark makes a more precise line than a pencil.
Unwrap, measure the length of the strip up to the mark, divide by 3.141 (π). This is the diameter of your syringe. The 20ml Once brand measures .9 in. (23.0mm), the 10ml is .7 in. (17.4mm).
The Simple-simple Flask
If you are not comfortable with the knife, this one is for you. Take a “sports-style” bottle cap. As these bottle caps are somewhat conical, you will find the proper diameter for your syringe somewhere down from the tip (have a few caps ready).
Now saw slices off the tip carefully with your razor saw until the opening is just big enough to accept your syringe.
You will probably have to carefully and slowly take a burr off the outer side of the cap.
Now you should have a perfect, somewhat tight fit. If the fit is perfectly tight, don’t test over and over. You will scrape the scale off your syringe, so confine your testing to the lowest end of your syringe.
Sand the cap inside and outside with the 220 grit sandpaper. Also, sand the handles and upper cylinder of your syringe. Then clean with alcohol. Put the syringe into the cap. Heat up your glue gun. Let it run really hot. You want the glue to flow. Heat the bottle cap and syringe with your hairdryer thoroughly and as hot as you can stand with your fingers. Any more might start melting the cap or the syringe. You do want to avoid this, but you want a warm cap to keep the hot glue flowing and bonding as well as possible.
This is really important. I had a few caps split from the hot glue at first. I noticed the hot glue partly rolled off the caps. This is when I started heating caps and syringe cylinder prior to gluing. I still would not entirely trust the bond. To find out, I made a new cap for testing. I sanded the cap and syringe as described, cleaned them with alcohol, and then heated everything thoroughly with the hairdryer. Then I quickly glued everything with hot glue. Some parts of the cap which didn’t bond well received an after-treatment with the lighter (careful!) Then I threw the cap into the deep freezer (0°F, or -18°C) overnight. The next morning, I took it out and quickly tried to get the glue to split from the cap, yanking the syringe back and forth. Nothing happened, no splitting. After all the abuse, the system was as airtight as before. So proper heating is paramount for a good bond and seal.
Caveat: Unless you land a “lucky punch,” the setup relies completely on the hot glue. If you apply moderate force or continued operation, the device may start to leak, as there is no mechanical tie between the bottle cap and the syringe. If you want to rely on the hot glue alone, refine your gluing techniques and test the arrangement thoroughly before hitting the trail.
You may, however, land a lucky punch by combining a 20ml syringe with a 1.3 in. (32mm) sports-style cap. Cut the conical tip off a Vittel sports cap leaving a screw-on ring that can just be forced over the cylinder of the syringe to make an almost alcohol-proof seal. A portion of the inner rim of the Vittel cap was just the diameter of my syringe.
This made a far better seal than any (tight) hole cut into a larger cap. Without any sealing, there was just a little dripping.
After applying some hot glue, the system was airtight. Because there is a pretty good connection between the cap and the syringe, this system will stay sufficiently tight. It can easily be resealed with a lighter should it leak. Rinse thoroughly with water before attempting to heat the hot glue seal with a lighter or you will end up hospitalized with severe burns. Any residue of alcohol left in the system will light up and burn. Also, take out the plunger first; it does not stand any heat.
It may pay off to go through a couple of differently capped bottles available in your supermarket.
You can also make this version with regular caps, but you will have to cut a circular hole into the bottle cap with the cutter you make for the other versions. The small pop bottle caps of 1 9/64 in. (29mm) diameter will only accept a 10ml syringe, however, as the bottleneck is too narrow to accept the 20ml one.
The Screw-on “Normal” version
This version should be as bomb-proof as ultralight gear. The syringe screws to the cap, is sealed with a silicone sealant, and is doubly sealed with hot glue.
First make your circular cutter. Cut about 1 1/32 in. (50mm) off a hardwood strip cross section of about 25/32 in. (20mm) x 19/32 in. (15mm). Use hardwood like beech or oak. Any softwood like spruce or fir will fail. Screw an X-Acto type blade to one end by placing two screws at the back, one over the sharp side of the blade. Measure exactly half the diameter minus half a millimeter of the diameter of the cylinder of the syringe you are using to the X-Acto type blade towards the center of the hardwood block. Drill a 1/16 in. (1.5mm) hole here to house your sturdy 1/16 in. (1.5mm) pin. Just make it tight and snug. You can drill other holes to fit other size syringes, or use this for other circular cutting needs and the stove.
Test your cutter on a piece of drawing paper and check whether the syringe fits. If it fits, the diameter of your cutter is probably too wide. Make another cutter.
If the hole (hopefully) is a tad too small, insert shims between the hardwood block and the blade. I added three layers of masking tape and one layer of heavy (200g/m2) drawing paper.
Now the syringe just fits through the hole.
With the 20ml syringe, it gets tight between the inner rim of your bottle cap and the syringe. I gain space by filing some material off the cylinder of the syringe, right below the handles.
The syringes used have a wall thickness of exactly 3/64 in. (1.0mm). Filing away half a millimeter on both sides poses no stability or leakage issues. If using a 10ml syringe, you can omit this step.
Look at your bottle cap. The inner rim makes a seal like a plug and has to be left intact by all means. Make a paper disc fitting exactly inside the inner rim of your bottle cap. Draw a line across the center of the disc, and mark the diameter of your syringe on the line. You see the diameter of my 20ml syringe marked here.
The self-tapping screws barely fit between the cylinder of the syringe and the inner rim of the bottle cap. I measured exactly 5/64 in. (2mm) from the edge towards the center (half the diameter of the head of my self-tapping screws) and marked with my sturdy pin on the bottle cap.
If you go with the 10ml syringe, just divide the distance between inner rim and cylinder of your syringe into two equal parts. That will help you decide what size screws and washers to select.
To cut the hole in the bottle cap for the syringe, remove the drawing paper shim from your circular cutter. I found the cutter to make too large a hole. Due to the flexibility of the plastic, the hole must be cut a tad smaller than on (stiff) paper. Put the cap back on the bottle to get a good grip on it and to prevent the cap from distorting. The caps usually have their center marked. Prick the pin of your circular cutter precisely in this mark and draw the circle. It is important not to apply force. Just a slight but precise scar on the cap is intended. Then go on, deepen the scar gradually.
When you are through, insert your syringe to check the fit. It should be a snug fit, no “air” between the syringe and the cap, but no forceful cap distortion either. If the cap slides down the syringe by itself, the hole is too wide. Just one shim of 200g/m2 drawing paper made the difference between the loose fit and the snug fit in the picture.
If the hole is too large, you may not get a tight seal. If the hole is too tight, you may open it up with sandpaper wrapped around a dowel. Go easy, a little at a time, and check with the syringe often.
Once you have your cap ready, drill two 5/64 in. (2 mm) holes at the marks near the rim.
Take the burrs off with your knife.
Your self-tapping screws should just fit through the holes. They touch. Do not distort the inner rim of the cap. Put the syringe in all the way. Center the handles of the syringe over the small holes in the cap and mark with Sharpie type of pen.
Turn the cap around and give the handles of the syringe a center punch with your awl exactly on top of the screw holes marking where to center your drill bit.
Also, mark the side of one handle on the cap and the corresponding handle of the syringe. Even if you work very precisely, it will matter which way you insert the syringe.
Take the syringe out and drill holes into the handles at the markings. The holes should be about the diameter of the core (not the threads) of your self-tapping screws: The screw threads in the picture have a 5/64 in. (2mm) diameter and the screw core has about a 19/32 in. (15mm) diameter. I drilled 1/16 in. (1.5mm) holes in the handles. Drilling your holes too small will split the handles of the syringe. If drilled too large, the screws will not fasten the handles.
Assemble the flask. If needed, the screws can be forced a little to find the holes, but be sure not to distort or damage the inner rim of your bottle cap.
Check for fit.
Take it apart again.
If you own a drill press and a conical cutter head, you can cut the hole for the syringe the way shown in the picture.
The drilling is easy when you are near the intended diameter. The photo shows the 10ml syringe at 11/16 in. (17.4m) diameter and my conical cutter only goes up to 25/32 in. (20mm).
Now you have both examples assembled and ready for sealing. Mounting the 10ml syringe is clearly is easier than the 20ml.
If you care and have the equipment, shorten your screws now. Once the screws have tapped their threads into the handles, they can be screwed into those threads without a pointed end. If you omit this step, you will have to cover the protruding screws well with hot glue. Do not attempt to grind the screws down after they are mounted to the cap. The screws will get hot, melt the plastic and tear out. The system will be damaged beyond repair.
Roughen the inside and outside of the cap, the underside of the handles of the syringe, and the top of the syringe cylinder near the handles with 220 grit sandpaper. Clean the areas thoroughly with alcohol. Apply silicone sealant sparingly to the underside of the syringe handle and the underside of the upper rim of the syringe. Apply additional sealant to the inner side of the bottle cap around the two small holes for the self-tapping screws.
Insert the syringe and screw it to the bottle cap. Don’t over-tighten the screws; just snug is enough. You are working with flimsy plastics. Scrape away any excess silicone. You only want a seal between the bottle cap and the syringe, not anything else. The silicone also does not stick to the plastic. It only forms a custom-fitted sealing ring, which has to held in place by other means. Put the project aside and let the silicone cure thoroughly, at least two days because silicone usually hardens slowly with moisture removed from the ambient air. It is not a good idea to remove any silicone smears and surplus later; you run the risk of pulling the silicone out of the fit between cap and syringe.
Clean the inside and outside of the cap with alcohol again. Heat the assembly with your hairdryer (see the Simple-simple version for the why) and seal thoroughly with hot glue. Apply hot glue to the top and inside of the warm bottle cap. Don’t overdo it; you will only add weight. Sealing around both the inside and the outside will do. Cover the screws well to avoid getting hurt during operation of the flask. Let the hot glue set well, leave it alone for about a quarter hour.
Systems: If you want, carefully cut away any excess hot glue, just chip off small flakes of glue if necessary. If applying force has the glue split from the cap, your gluing needs refinement. You need to work fast as long as the cap and the syringe are hot. You can try to reseal by heating the cap and syringe with a lighter, but take out the plunger of the syringe first, it does not stand any heat. Do not do that once you have used the flask with alcohol. Also, keep the flame well clear of the rim of the bottle cap, as the rim will melt away if overheated.
The Coupling-nut Flask:
If you are adroit with the circular cutter and X-Acto type knife, there is a quick and elegant alternative. Instead of screwing the handles of your syringe to the bottle cap, just stack a seal, a plug, and the syringe and screw the layers to your flask with a coupling-nut. A Coupling-nut system can be made from another bottle cap and is shown here with a water bottle and its 1 17/64 in. (32mm) diameter cap. One of the bottle caps is cut down to a ring (#2 in the pic), the other one to a coupling-nut (#3 in the pic.).
This flask is one for those who take a 10ml syringe. The flask with the greenish cap is such a system too (see #7 in the very first picture).
First, drill another pin hole into your circular cutter. You can use it to cut away everything off one bottle cap just outside the outer diameter of the bottle mouth. Go easy, you will need to do a second cut and do not want a loose center hole in the cap on which you are working. Then cut the hole for the syringe. The resulting ring, together with your syringe will form a plug to fit the mouth of your bottle (see #2 in the picture).
Slide the ring over your syringe and, with a small wire cutter, clip away the part of the handles which protrude over the ring. Clip several small flakes to prevent the syringe from splitting. File and sand without damaging the ring. Take the ring off. Sand the upper part of the syringe with 220 grit sandpaper. Clean the ring and syringe with alcohol. Heat with a hair dryer and glue the ring to the top of the syringe with hot glue.
Work quickly on a well-heated syringe to push the ring all the way up into the still hot and running glue. Do not touch the (hot!) glue; just push the ring.
Put some hot glue on top of the ring between the handles of the syringe. You want to have an even top rim of your plug consisting of a ring and syringe. The coupling-nut will press down around the rim, not just on the handles of the syringe. Even out the top rim of your system plug.
When the glue has cooled and hardened completely (wait), put the plug on your flask and chip off any excess glue, making an even outer and top rim of the plug.
Then you make the coupling-nut. Create a second circular cutter to cut a hole exactly the diameter of the plunger of the syringe.
Keep the required hole small; the smaller the better. (You may use a suitable conical cutter as in the example shown above). The coupling-nut will be forced over the head of the plunger, which is a bit wider than the shaft. This configuration prevents the coupling-nut from getting lost on the trail. After cutting the hole, you have to remove the inner rim of the cap.
Now you can assemble your system and check for fit.
Finishing all versions:
Measure the length of the tubing, bottle, plug/syringe system, and your awl.
Heat the awl with a candle or lighter and push the tubing over the hot awl to widen one end.
Repeat until the tubing fits snugly over the nozzle of the syringe.
Do not apply too much force in order not to avoid tearing the tube. Torn tubing will leak when you try to fill your stove. If it does not work, your awl is not hot enough.
Carefully heat the tubing a little below the syringe to give it a gentle permanent curve that will direct the tube to the point where the wall and bottom of your flask meet. Hold the system alongside your flask to estimate and cut the excess tube at a 45° angle.
Careful; leave it a bit too long. You can always cut again. Screw the syringe/cap system on tight and check for length. Repeat the cutting process until snug.
Give the lower end of the tubing a 45° cut on the opposite side to prevent the tube from sucking to the wall or the bottom of the flask during operation.
I had several tubes split after a few days. I suspect I forced those tubes a little bit too much when mounting them to the syringe. After some use, you should see to keep the tubing well above any of the ribs often found as reinforcements on the bottom of the flasks. Forcing the tube over these bumps everytime you close the flask stresses the joint at the syringe and may split your tube.
To avoid this problem, you can couple the stiff tubing with a short length of a (flexible) silicone tube running to the syringe. A 19/32 in. (15mm) length and 1/8 in. (3mm) inner / 13/64 in. (5mm) outer diameter piece of silicone tubing does the job nicely. Use fuel tubing from RC-model hobby shop. Make sure you push the nozzle of the syringe and the stiff tubing deeply into the silicone tubing so that they meet. You do not want the tube to flex. It is supposed to rest securely in the bend between the bottom and the wall of your flask, so that you can “snuffle” up the last drop of your fuel.
Congratulations, you are done! Four different snuffle flasks with their respective weights are shown in the picture. I think around 30g (1.1 oz.) for such a system is appropriate. The Swiss precision spring scale shown in the picture measured all the weights for the project. It’s not just a “guesstimator,” it’s a pretty pricey tool of precision. For gram weenies, you could save another .2 oz. (7g) on the 1 oz. (29g) flask if you use a 10ml syringe instead of a 20ml.
Now fill your Snuffle Flask with alcohol, taking the volume of the syringe into account. Close your flask. Turn it upsidedown, shake it, and apply some gentle pressure to check for leaks. You can see the level of alcohol just in the yoke of my hand between my thumb and my index finger. If the bottle leaks, try to reseal it as explained, or restart the process and try to do a more precise job. If there are no leaks, you are ready to go.
Unscrew the cap a quarter turn, so air can go into the flask when you operate the syringe. This process is not necessary on the flimsy and flexible water bottles, but well worth the trouble on the sturdier juice bottles.
Hold two fingers of your “bottle hand” over the bottle cap and the handles of the syringe to avoid placing any stress on the bond/seal between syringe and bottle cap when pulling the plunger. You will also avoid pressing on the bottle using this method. a tight grip on the bottle is likely to make you spill fuel, as compressing the flimsy bottle forces the fuel out of the bottle neck.
Now pull the plunger and fill your syringe. Then press the plunger back as required until the amount of alcohol you want to burn is left in the syringe.
Now unscrew the cap fully. Remove the system from the flask and empty the syringe into your stove. You can use the bottle cap as syringe handles. The force applied will only compress the seal and not tear it apart. With the coupling-nut system on a 1 17/64 in. (32mm) cap, you will have to clench the syringe between your index and middle fingers because the handles of the syringe are very small. There is no issue with a 1 37/64 in. (40mm) coupling-nut system, of course.
The long stiff tubing will come in handy to direct the fuel into any stove.
Take the system back to the Snuffle Flask. The flask is closed and ready to store. Light your stove and have a good meal!
If you are ready to refine your hot glue technique, the Simple-simple is a good choice. If you do not trust anything unless it is made solidly and is still ultralight, choose the “normal” system. If you are concerned about leakage, the Coupling-nut Flask is probably the best choice, even if it does not handle as smoothly as the other systems.
I found the coupling system to work pretty nicely for myself. Mounting the valve of a remote canister stove to a Lindal valve in cold weather, with your gloves on and without damaging the threads of the valve is a greater challenge than filling an alcohol stove using the Snuffle Flask. Plus, you have all the advantages of an ultra lightweight, low-carbon-footprint system, fueled by a replenishable, virtually non-polluting fuel.