Think in reverse. The black tank was one of the first things installed on the chassis to make it easy on the assembly line, then the house was built over it. Piping from the tank was assembled at the point it was easiest while the floor was being dropped on. There was absolutely no thought or engineering put into any future issues should they occur. I believe I would have already removed the wheel well tub, which is most likely slapped in with some narrow crown staples and caulk. Fernco connectors and long or multiple socket extensions are your friend.
