I am lucky that Haley does go in the bathroom when she has to. She goes on the throw rug right in front of the toilet. It's easy to clean and can be thrown in the washer when needed.
That's so funny about your friend's cat flushing the toilet. I remember many, many, MANY years ago when I was a kid -- there was a tv show called Real People. It was kind of a "news" show on at night, and it had interesting and entertaining stories about everyday people. The one (and only) story I remember from it was about a guy who toilet trained his cats. How great would that be??!?!