I'm sorry. I refuse to believe it would be possible to train a cat to use a toilet, despite what the CitiKitty company might claim. After all, you can't train cats to do anything. (At least, not my cat.) This is how the CityKitty Cat Toilet Training Kit is supposed to work:

The specially designed training seat securely sits on your toilet filled with litter. Your cat naturally uses CitiKitty as its new litter box. The rings are removed thus reducing the amount of litter. Once all rings are removed your cat is toilet trained!

I think the cat might use the citikitty thing while it has litter in it. But once the litter is gone, the cat will not keep going back to where the litter used to be. Instead, it'll pee on your bed (or somewhere else designed to punish you and force you to bring back the litter). But in the interest of fairness, if anyone has successfully used this device, I'd be curious to hear about it.