We recently purchased an auto waterer for our coop. It is mounted on the wall ( screwed in) so I'm not sure the best way to clean it.
It gets dirty pretty much every day. I cleaned it out once, but that involved syringing out all the water and then cleaning out the bottom. It was tedious, and didn't work all that well.
I believe it was meant for dogs so it is bowl shaped and the chickens love to perch on it.