What does this flush?

[JBM3M]

Not exactly sure just what this flushes. The gray tanks? The black tank? What is this "termination valve". My owners manual has nothing on this.

[chuckster57]

That is to clean the black tank. The Termination valve is the dump valve at the tank exit.

I leave my valve closed for about 2-3 minutes while running the rinser, just don’t walk away and forget.

[bobbecky]

It runs water into an internal sprayer in your black tank. The termination valve is the one you open to drain the black tank. There will be a check valve/air gap in the line from that hose connection to the tank. Some have had issues with that valve leaking, so you might keep an eye out for a water leak if you are using that system. The valve could be high up under the vanity sink or could be hidden in a wall cavity. It’s not required that you use the tank flush, but it’s there if you want to.

[JRTJH]

Here's a "basic diagram" of the black tank flush system. Your convenience center may have a valve to divert flush water but most do not.

As said, connect a hose (don't use the clean hose that you use to supply drinking water as it could get contaminated) to the fitting, turn on the water supply SLOWLY (so you won't "slam water into the anti-siphon valve) and monitor the process WHILE STANDING IN THE IMMEDIATE AREA... More than a few people have destroyed their black tank by forgetting or by getting occupied doing other things. If that happens, you're in for a "crappy mess"....