Carol,
I don't believe the "backflush" is really a backflush. I believe water merely flows into the tank at the top of the tank (curbside). Because the tank floor is sloped downward, toward the drain, it runs down, presumably carring any "matter" with it. There may be some spraying action, but nothing like spraying it directly with a garden hose.
I'm getting the impression that on some MH units, the toilet pipe enters the black tank & gets close enough to the floor of the tank that solids/paper can build up against the pipe & not be emptied at the dump station. This sounds like what happened to you.
Solution: ? Take a rough road home & dump at a facility near your home? If you are dumping & don't have a line of people behind you: Close the dump valve and significantly fill the black tank with water thru the "backflush" spray. Then open the drain. I know the next comment - who wants to spend longer than necessary there? Certainly NOT me!
That amount of "black, gunky" water seems like an aweful lot, though admittidly, with normal use of the plastic hose, I never see the rinse water condition ... nor do I desire to! Ha Ha Ha.
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