They are three-quart, double-walled, vacuum-sealed buckets set inside a pail on a 2" thick circle of foam insulation (yes, plastic) for the winter. They were originally ice buckets for cooling wine. They don't freeze enough to be hard to dump out (or thaw by adding hot water) within the 12 or so hours between times I do chicken chores until the temps are something under 15 F (-10 C). And then only over the night when the chickens don't disturb the surface by drinking. I went out three times on the few days it got really cold.
The buckets have very nice bale handles so they are easy to carry. I bring them into the house to clean them in the kitchen sink anyway. I thaw them there if needed. It was many mornings the first two winters - before I built the insulation pail. Then the buckets were set directly on cement block.
