A couple of years ago I got a polypropylene paint tray to use as a water dish for my Hermanns. I cut the ladder hooks off the front so it would sit level & it workes great. There's enough room for the big ones to soak & the smaller ones can get in & out easily.

I looked for another one but could never find one made of the same material until last week. Dollar Tree has 'em for only a buck so I bought a couple more.
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