The old wet bay used a flexible hose to send the water from the reel to the coach. Every time you wanted to backflush, you needed to hook up a separate water line. And it needed to be pressure regulated.
So I moved the pressure regulator inside the wet bay, replumbed the water, and added two valves… one as a main water supply valve and one for flushing the black tank. I added a second check valve to preclude any chance of black tank contents getting into the fresh water lines. Much simpler hookup, much simpler black tank flush.