I used the regular clay litter at first--I just put them in it once and they were fine. I have been buying clumping litter for several years now. I like it alot better because you are actually removing the little ball of pee so it isn't just stirred up in the pan to cause odor. I am kind of picky about the scent of the litter--I like Scoop Away, but only in Fresh Scent. There is one--I think it is multi-cat scent--that I smell constantly if I buy it. It's like I try to love on my cats and all I smell is their litter. If it bothers me--then it has to bother them--since their sense of smell is stronger than ours. I have heard that cats are picky about their litter as well. Hey, at least she went to the tub and not the carpet--good kitty!!