What type of litter do you use? If its clumping, then cleaning it out every two weeks is fine for one cat. If its the non-clumping litter..... yuck! When I use non-clumping litter, I dump it every other day for one or two kittens. For my adult cats, it would be every day. Thats a hassle so I never use the non-clumping

If its clumping, how often do you scoop it daily? Once? Twice? Some cats don't like to poop where they've already peed (and vice versa) so maybe a second box will help him.