I have a very hard water and hot water tank that is filled with sediment. It's very loud whenever it heats the water (sounds like small bombs). I've followed the instructions on the web to drain and flush it and while a few specs of rock-like gunk came out....when I fire it all back up....it is as bad as it ever was. Can someone help me understand how this is supposed to work? This rock like stuff doesn't float. It's heavier than water, right? So how would filling up the tank with some cold water and opening the valve get them out?