I've been using a vinegar-water solution to clean the pan since I first brought Cassie home. I throw a little baking soda in the clean, dry pan before I pour the fresh box filler in. She's so funny though, by the time I put the clean pan back in its place, take the old contents to the Dumpster, come back and wash my hands, I usually hear her pawing around in there. I think she just likes to be sure it smells like her!