H2H1 - 8/23/2010 3:46 PM just a little advice here,,, never open or leave open the gray tank open until you are ready to emphty both. The Black is open first and let drain, then open the GRAY to wash out the Black TANK waste from the hose. By doing this it helps stop the build up inside the tanks. I know I did it the way you are saying and it created a big problem until I was advised the correct way to do it.