Just got finished with my waterer. 3/8" did the trick. Once the burrs were removed, the nipple pushed in with a little persuasion. 3 for three. The fill valve I used in the 3 1/2 gallon bucket is mounted in the center through a 1 1/8" hole made with a hole saw. Nothing leaks and I have it hooked up to the water hose. I did already have the water pressure limited to 25 PSI using a pressure regulator designed for drip irrigation. Total price for the project was less than $35. This along with my 4" PVC gravity feeders make it where I could take a weeks vacation and come home to find the neighbors got 3 dozen eggs just for peeking in on them.
Now for the open-at-dawn, close-at-dusk coup door. I have an old, but reliable battery powered drill I plan to make into a screw drive system to lift and lower a door. As you can imagine, it will need to be light enough not to hurt them if they get caught, but heavy enough to pull down against predators. The trouble is, I do not know how to reverse the direction electrtronically.