Jwamiller, I have a similar situation. First off, I know my tanks and valves are mis-labelled. My black water empties by pulling the valve labeled "waste water". It's a silver handle, long rod located directly above the drain pipe. The other 2 valves are located about a foot aft of that, they are short stubs mounted up on the frame rail. One has a black handle but is labeled "gray water" and the other has a silver handle labeled "black water". My unit is at the dealer right now for a warranty worklist, and this is one of my items on the list. I do know this: I can only get 2 showers before one tank is full. Something is not right.