WHY does he keep doing that?! Argh.

My young male cat Thomas keeps going outside his box.

Before Thomas, I'd never owned a male cat before. Is this something he does to mark his territory? Or is he just being finicky?

I clean it every single day, but he'll still do it.

Is it 'going' or 'spraying'? If he's peeing outside the box he may have a urinary tract infection. If he's spraying, is he neutered? It may help, it may not if he's already started.

I agree about a vet visit, and the vet will want to know peeing or spraying. How many cats, how many boxes - sometimes even one cat will want two boxes - one for pee and one for poop. I clean at least twice a day - my boy will often wait for me to clean. Also, sometimes they just don't care for the litter - if you get an all clear from the vet, you might want to try a separate box with new litter. I had great luck with Cat Attract litter when my boy had issues.

Also, are you cleaning with an enzyme cleaner - I had good luck with Nature's Miracle and Zero Odor.

Try and stay calm and patient as you try and find out what's triggering the behavior - believe me, I know it's hard!