UL MYOG hanging water bag?

I have thought about this, but have not tried it. If you find an adapter that works, please report back!

Maybe something like this could work.
Metaland Bulkhead 1/4″ Hose Barb Plastic Polypropylene Thru-Bulk Fitting for Water Fuel Air (Pack of 2) https://www.amazon.com/dp/B08MPLSGSR/ref=cm_sw_r_cp_api_glt_fabc_J6P8W3046PNA9ZNC3HT4?_encoding=UTF8&psc=1

Try a farm supply store. They have lots of small fittings for animal watering systems. Regarding the bag, you could just use a dry bag or how about one of the silnylon buckets from Sea to Summit? I added a one way air valve to a silnylon sack to pump my sleeping mat. Melted a hole, stuck a reinforcement patch on with silicone sealant and then glued in the valve. Has held up to pumping so far. The other option is the old Ray Jardine method, just insert the hose from the top of the bag and siphon over the top by getting the flow started by sucking on the tube. You’d need something to tie the end of the hose to the bottom of the bag to keep it below water level but it’s an easy way to try out the system.

+1 on the siphon and a light silnylon bag.  Less chance of ripping or leaking.

On the subject of avoiding leaking and ripping, you could just use a small silnylon “tarp” and gather the ends to capture water like a bag, then tie it off at the top with some cordage, slipping the tube down into the bag before tying it off. I may actually try this, could probably just use a 3″x3″ square of silnylon. Like a “Hobo Bag”

These are all very good ideas.  siphon would be fine and doesn’t have a plastic connector to break. I’m trying this with a sil-nylon dry bag asap

Sea to summit makes a pocket shower which alone without the heavy pouch weights less than 3oz IIRC  not sure how to convert the shower head maybe stretch something over it. Ray Jardine used to have what he called a hikers friend water filter system made out of round piece of coated nylon and filter layed inside

Another possible option for the storage bag are these (chicken oven bags):

These are incredibly strong for their weight (8 grams) and are also very multi-use (stuff sacks, sock VBLs, meal storage, mini solar green house–for preheating a black water bottle, etc.).  I once made a 2 gallon bucket/bag with one–using Leukotape  for  the carry handles.   Might be a fun (and cheap) project to test.