John,
You can move the panel out far enough to get a hand behind it to disconnect everything from the panel to remove it. The water manifolds will stay in place after the 4 clamps (2 for each side) are removed. The knobs just pull off. After the panel is removed, you can see how the tank outlets and dump valves are hooked up to the outlet "Y" fitting.
Some of the SMC coaches did not use a standard "Y" fitting because they drained the washing machine directly into the sewer outlet, so on those coaches, the top of the sewer outlet "Y" has a 3 inch fitting out one side, a 1 1/2 inch fitting out the opposite direction, and a 1 inch fitting going straight up for the washing machine.
Gerald