This happened too me recently when I set up my 180. The cat jumped about 5 feet on the ledge then down into her new expensive litter box. Of course I didn't realize this until I got home that nite and saw all the cat tracks in the new sand. I wasn't about to waste sand at $20 a bag plus shipping. So I rinsed with water and all is good, plus I figure a little cat pee to 200 plus gallons of water with the sump, etc.