I have a flush toilet which is not sucking down waste as it should. After looking at the filling tank I've noticed that the wayter don't fill up to recommened water line. It stops roughly 2 1/2 under it. Ive held down the float arm to let water rise and then flushed and it seemed to be a lot better but still not perfect. How could I ge the water to fill to this recommended line on every flush? Your answers will be appreciated.