Carmello had a dirty bottom too (check Poopy bottom kitty in the grooming section) .
I got a lot of advice here. One person said that she puts her cat in the shower with her and washer her bum. A few others said baby wipes are the key. We actually used clippers to keep his fur shaved down
. We have not had this issue in just 2 weeks now
My guy says adding less litter is the answer. I give him less wet food too. Also Carmello understands when we tell him his bum is dirty
and if we tell him he will go and clean it
. Amazing I know, but it works for us.