Apparently you do it in stages and begin with draining the water out of your toilet and filling it with cat litter, then i suppose you keep reducing the amount of litter and then introduce water. I presume you'd need to have more than one toilet available for this stage unless you are happy to scoop your own *** out of the litter as well as the cats.
I can see that being workable though. Getting them to flush and then wash their paws is probably the hard part...