[Chester Stone]

I would like to verify if I am using my dump valves correctly. There is an air valve on both sides of the coach that empties into the drain hose. In addition the is another valve which seems to be connected to the main tank. On my 2001 coach, this manual valve has been replaced with an air valve. I assume if I want grey and black water to mix into one tank for dumping, I leave this tank valve open. If I want to accumulate the black water in one tank, and grey in another, I should leave this valve closed. Is this correct and is it practical to accumulate the black water in one tank and save the grey water to flush out the sewer hose?