I'm getting very tempted to try and get into a wall that houses the black tank flush water line. I am pretty sure it's leaking at a fitting that it up in the wall, and cannot be pulled down. When ...
You can find those panels online in several places. Cut the hole from the middle of 2 studs and make a patch panel that overlays the entire hole. Wrap the edges with seam tape and it will look like a factory install access panel.
