I use both galvanized and plastic waterers. Little Giant(Miller Mfg) used to be the best 1 gallon plastic waterer around. You could fill 4 and carry them upside down, two in each hand to the pens. A couple of years ago they changed the design and now if you try that you have two gallons of water on your foot because the threads will not support a gallon of water. I do use the 3 and 5 gallon Little Giant waterers with the screw on lid. The O rings as they are placed by the manufacturer does not always seal well and they will leak. Take off the O ring and put it in the lid and let it seal against the top rim. Problem solved. My galvanized waterers are one&a half Gallon hooded waterers that are sold for Pigeons. I have a lot of them(50+). Some I have had for 30 years with no rust. Some that I got last summer are already rusting badly. It seems to depend on the quality of the galvanized material used by the manufacturer whether they rust or not. I usually buy a dozen at a time and I cull them much like I cull my birds. If they start to rust quickly I take take them to the auction and get rid of them. I have several with a little outside rust on the bottoms but none with any inside rust. I do like the plastic better for the ability to sterilize them easier, but the Galvanized are fairly easy to sterilize also.
