Mine do that too. It seems snakes can't be litter trained, or at least >>>>>> over there trained. I'm working on an idea for a moist hide that won't involve buying products that get urinated and poo'd on. It's simply an idea in my head at this time.
I'm going to use small litter pans, like for cats and cut out the bottoms partly. I'm going to zip tie or brad in several layers of chamois. Hopefully, this will be a way to get it wet once and have it release moisture continuously for awhile. I don't know, we'll see.