Have a pair of the same and agree with BiW, just change it daily. But then it only stays clean for a few minutes anyway! Ours have a drinker that is quite deep and they can get their heads submerged in plus a trug to bathe in. At least they can't poo in the drinker.
Hope you're enjoying them and the eggs as much as we do. Fab for baking lovely sponge cakes.