Drip, Drip, Drip. That is what John saw when he flushed the black tank. Where is it coming from? Since we own a Montana 5th wheel, he went to the Montana Owners Club forum, searching for advice. From other posts, it sounded like the back-flow preventer in the black tank flush line was the problem. However, the forum posts were all about RVs with the kitchen next to where that line runs. We didn't have a pantry wall to open up. We picked up the appropriate part from RV Traders, a Montana dealer in Mesa, and also made an appointment for late in March, in case John couldn't fix the problem.
After looking and calculating where the part might be installed, and reading a post that said they found it by removing the faucets in the shower, John found the proper location. That meant taking the TV off its perch.
Next step, cutting a hole in the back wall of the TV cabinet--after moving the sliding door that goes into that wall.
There is the offending valve. We even ran the tank flush water to confirm it was leaking. It was.
He removed the valve (while I continued to hold the TV),
and installed the new part. We again ran water through the line--no leak! Another problem solved.