My toilet has a problem with flushing. It flushes right half the time. The other half it either plugs or almost plugs. When it looks like it will plug I just hold the handle down until it either plugs or it flushes all of a sudden. It very seldom runs over where You have to shut the water off. So I don't know if I have a toilet problem or plumbing problem or what. Any suggestions? I think it's an American Standard.