[Motor31]

On the earlier models the check valve was located in the wall behind the shower. There was a square panel inside the pantry that could be removed that gave gave access tot he lines and valve. On my rig that was never tightened up at the factory and later I had to replace it entirely. Look in the pantry area along the common wall between the bedroom and the room outside the bedroom. There may be a square panel held on by screws. Remove the panel and see if you find a couple lines that have an "L" shaped valve installed in it at the top. The valve was installed to be at the top so it can drain.

You can check to see if the hose connections were tight or if the valve is in backwards.