man I wish I could train mine to do this. I hate fucking with litter boxes. If you poke around youtube you can find videos that explain the process. But as already mentioned, there's risk of some pretty nasty messes and the training process is gross too.
There are litter trainers you can get for that, I think its called litter kwitter or something. A friend of mine had one and used it successfully. What worries me about the whole process is that some cat bugs have been known to be resistant to water treatment processes.
