Pooping in tub, peeing in the drain
(Oak Creek, WI)
Seriously, one of our older male cats poops in the tub, most of the time leaving a horrible stain which cannot be removed! I've witnessed him 3 times peeing above the drain. Is this due to the S-pipes which sometimes smell like, well, a toilet?
I think it's possible that he might be drawn by the smells and views it as a kitty toilet, Kathy, or it could be something else. When cats get older they sometimes get a little off, or he might be having a spat with another one of the cats in the house.
Litter box guarding is a real possibility in multi-cat households. Sometimes it's serious, and other times it's just one cat playing with the other, but then one of the cats gets tired of being harrassed and finds another place to do his business. It's also possible that the litter box isn't clean enough for his preference.
The usual rules always apply, of course. For example, I would make sure you've got enough boxes, that they're squeaky clean (and that includes replacing older plastic boxes periodically that have absorbed odors), in the right locations, etc. Think about any changes in his life or in the house that may have triggered a behavior problem, and make sure he has no medical issues.
If you've done everything you can to cover all the bases, then I suspect the best thing to do is restrict access to the tub (or the room). The alternative would be to try confining him in a room or a cage and doing isolation retraining.
I'm sorry you're having troubles and I hope that helps a bit.