I'll bet it has a small reservour with an air assist inside. We have one like that in our guest room. It would allow plenty of room for fish as in the picture. They're pretty powerful, very water efficient, LOUD and expensive. If my plumber friend didn't hook me up, I wouldn't have spent the money for it. I'd be scared to flush it while sitting on it. The **** thing sounds like it would suck you right in!!