we had some flushable kitty litter, but we didn't actually flush it. I don't remember the name (sorry!) but I didn't care for it much. It made our whole upstairs smell like a porta-potty. There may be a different kind that isn't so bad though. I would just try going to a pet supply store (we go to Petco) and looking for some that says "flushable". There will probably be some there. sorry I can't be more help!
There is some wheat litter that is clumping and flushable. I'm trying it right now, and it seems to be ok. However, I haven't flushed it because it's easier for me to put it in the trash.
I flush my feline pine. I really like it and it really cuts down on the smell. If you do have a septic tank, it may not be the way to go but if you live in the city then I would recommend it.
I saw an ad for a flushable litter in this month's Cat Fancy. It's called World's Best Cat Litter. Their website says they'll tell you where you can buy it.