T.S.
Take him to the vet first to rule out anything medical. Second, to discourage the peeing, put kitty's litterbox where the drain is and over a series of days/weeks, slowly start to move the box back to it's desired location. Also, think about reasons why he might be acting inappropriately (new litter/person/pet/did you move furniture). Cats are creatures of habit and anything new or changed could trigger this. Also, I would get a plastic mat and cover the drain so the pee is easier to clean up in case he goes there again.