While there is nothing wrong with my dump valves, I added an end of line valve for several reasons.
1) If a dump valve fails to close for any reason (TP in the valve, rolled O-ring, etc), I won't get my "feet wet" finding out.
2) In an emergency, I can partially dump my gray tank water into the black tank by using the closed end of line valve to make a path to the black tank. As long as you don't get greedy and let them equalize, no black water should enter the connecting pipe. Just fill the connecting pipe with gray water first; then pop open the black tank for a few seconds at a time so the push is into the thank.
3) Makes cleaning out the tanks easier when using the turbo flush.
4) FAST closure of the dump mast if you overfill your blue boy due to inattention. The spill will be limited to the short hose (8-12 inches) from the shutoff valve to the blue boy inlet; rather than the entire dump mast plus the hose.
Also replacing the sewer cap with one that has a hose connection will allow dumping of gray water using you "black water only" hose at campgrounds which allow gray water dumping into gray water pits without using the larger sewer hose that gets everyone upset you might be dumping black water, too.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW