This instructable stems from my being lazy and my very large dog that drinks lots of water. I doubt this idea would scale down for a small dog but it works great for for 5 gal buckets. The photos i have taken are actually from disassembling and cleaning a water bowl that i have used for over 3 years. This is a pretty simple build.
Galvanized tub (about 5 gal)
Diaphragm style toilet bowl filler
12" toilet bowl supply line
brass garden hose female fitting with 1/2 male barb
1/2 to 3/4 inch hose clamp
Power drill and 7/8 bit
Drill a hole in the side of the tub, so that the diaphragm on the filler sits as low as possible. For me this was about 3 inches up from the bottom. I used an old junk 7/8 spade bit. It would probably help to clamp a scrap of wood to the inside of the bucket, but i was able to punch it though just fine. Also a file to clean up the edge would help if there are any barbs.
Simply mount the diaphragm filler in the hole with the diaphragm facing down. I found it best to use the rubber seal with the kit on the inside of the tub. Just cinch it down until its tight.
Take the supply line and cut off the compression fitting. Then slide on the hose clamp and work the barbed fitting into the cut off tube. Its a pretty tight fit so it takes some work. Tighten up the hose clamp to hold it in place. Screw the plastic end into tub and the brass end into a garden hose.
Turn on the water. when the bowl gets close to full use the adjusting screw on the valve to get the water level just right. With a little tweaking you can get the bowl to fill right to the edge without overflowing. I will go out once a week and tip the bucket over just rinse it out and get all fresh water but other than that i never mess with it. 3 years and still working great!