i used to have a cat that would potty in the bathtub. we took her to the vet and everything checked out fine, we tried the retraining her thing, we put her in a room with just her food and the box, and she used the box instead of the tub, but as soon as she was let out she would go back to using the tub. so we kept a real close eye on her for a few days, and it turned out she would use the litter pan right after we cleaned it, but as soon as another cat steped foot in it she went right back to the bathtub. we had to seperate her from the rest of the cats, keeping her upstars and the rest of the cats downstairs. we still let her go downstairs for visits, but her problem was fixed by making sure no other cats used her box.