I use Swheat Scoop which is flushable. You have to let it soak, though (I believe the bag says at least 5 minutes, but I like to wait 10 minutes) before you flush, or else it'll block the toilet and you get a brand new pool in your bathroom. The toilet upstairs works like a charm, but I found out that the toilet downstairs has a smaller hole where the waste disappears through (know what I'm talking about?), and I quickly found out I have to increase the soaking time with that one. I had several close calls where the water rose nearly to the top (I was scraping away frantically with the scooper, trying to clear out the hole at the bottom of the toilet so some water could escape, lol).
Dumping the waste in there and then immediately trying to flush isn't a good idea. You have to give a little time for the pee balls to sort of saturate with water, so that it breaks apart. Swheat Scoop is made entirely of wheat, so I don't worry much about it clogging the toilet. I DO worry when I get lazy and try to flush too soon, lol