Sewer Flush - do you open just black tank or both

path1 wrote:
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.

I do that too, but leave the black tank valve open for about 10 seconds and then close it when draining the gray. The splashback from the gray dump tends to clear the grunge out of the black valve and the soap leaves it sliding smoother.

On my HR the factory installed tank flush is only on the Black Tank, I have a Valterra Flush King I bought that will cause a surge of water from the city water to rinse the tank, 3 min. and flush, do this a couple of times then I close the black tank valve and open the grey valve, (it is open most all the time) then I can back flush the grey tank a couple of times, you woul;d be shocked at the little pieces of junk that is in the grey tank, a couple of flushes and no smells.

Theoretically, if the black tank had more in it than the gray tank, and the gray and black tanks were opened together, the black tanks contents could end up in the gray tank if the drain hose didn't drain fast enough or had a blockage. That is not a pretty sight. LOL

And believe it or not, boondocking one time where there was a gray waste water collection thing, this guy was telling us how he puts on the termination cap and opens both valves so black tank runs over into gray to extend his boondock time. Not a bad idea IF you have "P" traps in all gray water drains but mine doesn't and I don't think most do. Shower drain usually doesn't and don't want to smell that. I think I did misunderstand your question at first. Yes sewer flush is just that to flush sewer. Maybe it should have better name of Black water(holding tank)flush.

I think the OP is only talking about which tanks to open while using the tank flush system, not about the order in which tanks are drained.

path1 wrote:
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.

That is basically the way that I do it. I also like to flush out both tanks with fresh water when I get home. The black tanks always gets drained first and the gray tank second.
A lot depends on the way that they are piped. Theoretically, if the black tank had more in it than the gray tank, and the gray and black tanks were opened together, the black tanks contents could end up in the gray tank if the drain hose didn't drain fast enough or had a blockage. That is not a pretty sight. LOL

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.

No harm but no reason to do it. The tank flush is to flush the black tank only.

The flush only goes into the black tank on my Montana. No reason to open the gray tank.

No harm. The flush just squirts water into the black tank.

Black then use the gray to Rinse the drain hose.