Is there a better way to get powder into a drinking container?

Instead of pouring it out of the top of the ziploc, cut a small bit off a bottom corner, much easier to pour from.

Spoon?

Here's a workable solution—

If you keep a journal use a clean page and fold it down the middle and put a tablespoon of powder in the fold and use it tilted as a funnel into the bottle. Shake it clean and return it to the journal.

What is the diameter of the receiving container? Larger will make it easier.
Ziplocs suck to pour from since the powder gets into the groove and then does not seal well plus material does not pour well over the lip. How about not using a ziploc?

I like the funnel idea.

Doesn't seem to matter the diameter of the opening. Even a jar will have the same problem. The powder, depending on its properties, will clump and not flow, then a whole clump will go "fumph" and get everywhere. A paper funnel might work. I don't like the idea of cutting a hole in the corner of the bag. Then I would have to individually wrap every serving of milk or protein powder and that's just too many bags, too much waste and not allowing for whether I feel like adjusting the portion size.

You could always roll a paper funnel, it would be fully adjustable to the opening.

Doug, you're a flippin' genius! Perfect solution.

"Then I would have to individually wrap every serving of milk or protein powder and that's just too many bags, too much waste and not allowing for whether I feel like adjusting the portion size."

Not trying to convince you, but, FWIW, not entirely true. As long as you can roll the bottom a couple of times, which in effect 'closes' the hole, you're good. So the ziploc part becomes the bottom, the long side with a hole cut it in becomes the top, you roll it a couple of times to close and secure with a rubber band. Works for me.

"Doug, you're a flippin' genius! Perfect solution."

In the 'credit where credit is due' department, it was that old, crusty Tom K. who mentioned it to me (and I'm sure he was laughing at me at the time) as he, with a bemused look, watched me make a mess trying to pour some powder into my water bottle on our Sierra trip. If I recall correctly, he waited until I was done and had made a nice mess before mentioning it. :-)

Repurpose a copy-machine tone refill container. Designed and used for transporting VERY fine powder and then dispensing variable amounts in small openings.

Wash the hell out of it, first. Duh. I'd suggest running it through a few dish-washing cycles.

If not, MYOG an adaptor for a wide-mouth container (Gatoraid bottle?) but epoxying a section of funnel or sturdy straw onto a SECOND cap. Transport the powder with the original, intact cap. Use the second cap to dispense the powder.

Perhaps I'm misunderstanding something about what you're doing… but why don't you use a spoon?

On the PCT I used hundreds of bags of Malto powder. 8 found it very easy to pout into a 32oz gatoraid bottle. You can also use Doug's method but I generally tried to keep the bags intact for trash.

Since 2011 I switched over to keeping a dose of malto mix in a 16-20oz lightweight water bottle. the advantage of this setup is you can fill the 32oz. Bootle halfway then turn the water bottle up and put the spout into the gatoraid bottle. Why is this nice? It allows you to swirl the gatoraid bottle as the powder flows in getting a much better mix then just dumping the whole amount in at once. this is especially helpful when mixing at higher concentrations.

Another nice feature of using the water bottles is I can put two into each side pack pocket. they are virtually indestructible, other than by bears and are waterproof.

is a coffee measure and a funnel. I've got my drink mix figured out so that I use one coffee measure per liter. If no measuring is involved, making a funnel out of a plastic bag is a good alternative. Cut the bag on the diagonal and then cut the corner off. Holding the bag over the receiving bottle, pour the powder into the bag funnel and wash it down with a bit of water. If measuring is involved, then a spoon and a plastic funnel might be worth the weight penalty. I would rather carry a measuring spoon and a light weight funnel than to try to pre-weigh and bag each dose. Clean up with a rigid funnel will always be easier than with a plastic bag funnel.

I spill just as much using a spoon as I do using any other means of on-trail powder measuring and mixing.

I suppose I could fill up a plastic bottle full of protein powder and another full of milk powder. At home I'd have more patience with the tediousness of filling it, a more level surface, less wind and even the opportunity to recover any spilled powder. If it flows out of a plastic bottle fairly well, that might do the trick.

Could you mix both powders together into a container? This way you would only have to open one container and not worry about spilling so much. If the powder mixture is in a bottle, then you can give it a good shake and roll to remix everything if needed.

Plastic bags are not all that reliable. Powder tends to stick by electrostatic attraction. Then it goes everywhere 9sometimes).

Paper and alfoil on the other hand are fine. A cone of paper is definitely UL, long-lasting and reusable. Alfoil can degrade, but works a few times.

Cheers

Make a simple paper funnel. Take a square piece of paper, fold in half, then half or thirds (like a cone). Snip the point, and you have a funnel.

If you make it out of wax paper, it will stand getting wet without falling apart.