I have a large barrel with a tube and a nipple waterer. It is important that there is a hole at the lid because otherwise a vacuum is created. It is just a simple system using gravity mostly. I do have to clean it and change out the water weekly and sometimes I fill it with ice on really hot days.
I have also used nipples with cat litter bins. I also used a tube because it was easier to set the bin on a shelf and have the tube dangle than to instal the nipple directly. We try to repurpose those bins - my husband also sometimes paints them and uses them for planters.
I've had alot of luck with auto watering cups. I have a low pressure gravity system using 1/2 inch pvc, 3/8 ID tubing, and a 5gal bucket suspended a couple feet above the waterers. I have three cups for our dozen turkeys and it works great. They go through 5gal of water in about three days, and its always fresh and clean and they never get litter in the cups which are about 18 inches off the ground. They entire set up cost about 20$ to build including the waterers and required brackets. The best price I found was Cutler Supply, here's a link.
I use float valves. I have a pan that is about 5 inches tall and I attached the float valve to the pan. I ran a hose from the barrel to the pan. My rain barrel is about 10 feet from my chickens pen. It works well except the second float valve didnt come with a rubber seal! Of course you dont notice because its inside so I guess I have to get another one, but it works really well for me. Plus float valves were only $6 on sale.