Cutting into a wall, ideas/closing back up

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 using the black tank flush water runs down the line from this location, as best as I can figure that's the high point of the route.

I'm looking for suggestions on the best way to get into the wall. It's a wall between the bunk room and kitchen. Closed off with the very thin, decorative panel material. This material is stapled into the wood frame all over the place. Pulling the stables is either way too involved, or will likely destroy the piece in the process.

I was thinking of cutting an access panel of some kind, but then am wondering how to best patch it back up and finish it so it looks clean. Any personal experiences like this?

Thanks