Here is a pic of a built in black tank flush check valve that I found zip tied up behind the shower valves.
After getting my suite I thought it was wrong not having a check valve at the flush inlet. The water would run out when I unhooked the hose after flushing. I did not know that there was one built in the suite.
So I bought an inlet with a check valve in it and put it in.
I seem to have the problem fixed now.
The problem was that there never was a screen on the inlet washer and sand and grit got up into the built in check valve and caused blockage.
I pulled the shelves out of the pantry to get to a couple access panels that were screwed on in there and I was able to cut the zip ties that were holding the flush hose. I removed the built in valve and filled the black tank to the top and back flushed the hose from the black tank flush.
Then I re-installed the hose connector with the check valve and everything seems fine.
I just thought I would post this for others that may have this problem.
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