I use 2 of the largest I could find, hooded pans, sometimes they like to pee standing up!I use plain clay litter, (Cat's Pride) scoop solids at least once a day, more if needed & stir the whole thing, helps keep all dry.Pans get dumped & washed & refilled every 3 days, had to do the same with clumping litter. A month it's supposed to last? No way, just as stinky as the less expensive clay in 3 days, that's been my experience anyway. (3cats,2 boxes)