[DQDick]

[quote]Originally posted by ajjoez

Our grey water goes into the black water tank. When I drain the black water, I close the handle and open the grey water and it helps clean out the black water hose. ajjoez

What your are describing here is what most of us do. When you shut the black water valve it's shut, but stuff is still in the drain pipe after the valve. When you open the grey tank it then floods the sewer pipe and cleans that out. It doesn't go thru the black tank it goes thru the shared sewer pipe.