Just about to build a new one. Here's some wisdom from what turned into problems.
It's tempting to put poultry cups right into the 5 gallon bucket (or whatever) but eventually - the plastic will crack - pick that bucket up when there's too much water- and it will distort the shapes and voila! Leaking bucket.
My new idea I'm going to try in my brand new coop will still consist of a 5 gallon bucket.
I'm going to use 3/4" PVC and Uniseals for the 3/4" PVC - and kind of like spokes on a wheel, I'm going to put around 6 Uniseals in the bucket, then do about 4-6" of PVC pipe, and then will screw the poultry cups directly into the PVC where they last a LOT longer with many fewer problems. I've had way too many leaks with screwing the poultry cups into the 5 gallon bucket. I wish they'd make the horse-grade buckets with secure lids - that plastic is thick enough to reliably hold a poultry cup- but the lack of a top defies the purpose, so I'm stuck with the typical 5 gallon bucket.
In case you're not familiar with Uniseals, they are magical devices that you push into a 1 1/4" round hole in a bucket - no caulk - no tape- no nothing - stick the pipe (3/4", 1/2" - I like 3/4" because it allows for more water flow) through the center of the Uniseal … and it holds the water back. The only leak I've had was (drumroll) …. the bucket cracking around the Uniseal from me picking it up while it was heavy too many times.
Each "spoke" will have a ball valve on the end so I can empty the bucket in a hurry, and will have 2-3 poultry cups per spoke.
Probably not a great description but I'll take pictures once I'm done with it.