Maybe just me...When dumping after hooking up drain hoses, Pull gray maybe 2 seconds to make sure No leaks (gray spill easier to deal with than black). Close gray. Open black, wait till empty, close black. Open gray, to get most nasty stuff out of drain hose. Close gray. Keeping your drain hose in sewer hole, rinse your drain hose. Water in top and shake your hose around, maybe 30 seconds. Remove drain hose put where you store it. If anybody in line, drive away! If nobody in line and your the type that likes to give your tanks a water massage to get out the last spec of whatever go ahead.
