[Bad Moon]

Get a twist-on valve from Camper World or Amazon, about $20. And a clear elbow for about the same. Elbow allows you to be sure tanks are completely drained. After you dump the black tank, close the twist-on valve, but keep the black valve open. Then open the kitchen grey-water valve for about 15 seconds and close it. This allows kitchen waste water (mostly clean with lots of detergent) to flow into the black tank. Now open the twist-on valve. You will see grey water first, then lots of brown water. Repeat this process several times. Then do the same thing using the bathroom sink/shower grey water tank. Finish up with the tank flush. Save enough bathroom grey water to flush out the sewer hose. And be sure all the valves are closed before you leave! This is the best way I have found to clear the maximum amount of gunk out of the black tank. I complete the process with chlorox-calgon-laundry detergent (about 1/2 cup to 1 full cup each) with a couple gallons of fresh water. This mix will slosh around when you drive and help wash-down the walls of the tank.

The side benefit of the twist-on valve is no more "leakage" on my hands and feet when I hook up the sewer hose. Belt and suspenders!