It's just a standard 5 gal water bottle that all the office/home water coolers use...
I fill it thru the neck with a large funnel & scoop...then flip it over into the top of the 3" PVC pipe and let it do it's thing until the feed disappears into the PVC tube and refill again.
since it's a clear bottle, no guessing or opening the feeder to check when the feeder is getting low/empty
and no way for any critters, bugs or water to get into the top of it either