Just a heads up for anyone with a new rig. First time we used the black tank flush we ended up with water in the bathroom. Turns out that whoever installed the unit somehow put it together wrong
. When we turned on the outside water to flush the tank, water came out of the top of the one way valve. Took it apart to discover a spring and ball that were in the wrong side of the valve. Moved them to the other side and no more leak.