We've got a lovely male Siamese, 5 yo. Beloved bought me a 3 month old Bengal kitten in early January. Siamese goes out through catflap. Kitten took to a litter tray with no real difficulty, although on half a dozen occasions he has fouled the kitchen floor, a rug in the living room, and has left a pile on our bed (grrr)
Now he uses the catflap too, and we've transferred the litter tray outside the flap. Sometimes he'll use it, but he's peed twice in the kitchen today (and once on ds's High chair (double grrr) and crapped twice on the (now discarded) doormat.
Any suggestions on what to do? He's in fine health, and not at all intimidated by the very placid Siamese. Dw says if he does it again, he'll have to go