This can vary widely depending on the animals, their diet, the size of the enclosure compared to the size of the animal, etc etc etc. I rarely clean out my natural tanks. When I had my mixed tank up and running, I never cleaned anything but the water. That tank was HEAVILY planted though, and that's another factor. Another example would be an animal like a water dragon which almost always goes in the water, in that case, you just have to do more frequent water changes.
So, like I said, it all depends, lol...
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