I put a plastic bowl in there and filled it with litter. Floppy and Robocat used it, but Daisy didn't, so it didn't work out. You're supposed to get them using the litter, then remove the bowl, and it worked with the kittens, but Daisy never caught on when the bowl was removed, so it foiled me when I had to put a litter box out, and they started using that instead of the toilet.