I couldn't train my kitty to use the toilet, I would be much too worried about them slipping in. The basin of a toilet bowl is extremely slippery and the cat may not be able to get out. Try wetting your kitties paws and see how well he can walk in the bathtub, it is very different than when their paws are dry.
There are a lot of people who are "confident" their cat is not in any pain when it is declawed too
, I always ask them "did your kitty tell you so?"
I don't eat off my floor, so I am not too worried about it being perfectly sanitized, plus I use clumping litter, boxes are cleaned and kept filled daily so they don't walk in soaking litter.
Feed your kitty a raw "natural" diet, you will find their poops won't stink.