Simplistic Solution
This is definitely the most basic solution to filling pots and buckets, but I just picked up a
shaker siphon at Lowe's for $6 dollars. This is an amazing price because I paid $16 for my last one after looking everywhere for them (even Lowe's where the workers said that they had never seen or heard of these before... it was the same Lowe's). I marked one for gas, and now one for water. I'm going to work on setting up a valve and sprayer nozzle for it. Should work to initiate the vacuum so long as the valve and nozzle is open when shaking, and then closing the nozzle. If this seals enough to hold the vacuum ready then water should be ready on-demand. Right now I just break the vacuum when I don't need any more water. It doesn't take much shaking to get it going again, and it is very fast on delivery.
I use the
Reliance water jug that you are talking about without issue. No leaks, hasn't cracked, I've only been satisfied with it, but I have heard other reports. For me I can't fit a shape like a 5gal water jug, so the shape of the 7gal Reliance works best. That's the issue with having such a small rig. Also, the spigot on it is really convenient.
I also just set up a 2gal bug sprayer hot water shower for less than $34 at Lowe's. They had a nice bug sprayer that was on clearance for $19, then I just added a 6ft braided hose, hose clamps, teflon tape, an elbow joint garden nozzle adapter and a garden nozzle sprayer. It works phenomenally, seals up perfectly, and heats very quickly on the stove. I'm going to pick up an slap-on aquarium thermometer to monitor the temperature very soon. The elbow joint allows the nozzle to hook around a rack, branch, or use some rope to hang the shower nozzle above. Thinking about tapping the handle of the nozzle lever, and hooking up a string pull so that we don't have to reach up to rinse. The nice thing about the set-up is that the pressure is variable at the nozzle. Also, considering tapping a presta valve on the tank, so that it can be compressed using the compressor on the truck. Pictures of this soon.