[Richard]

I am with Micheal if this coach is new to you. Newell uses a unique setup on the waste tank dump valves that is counterintuitive until you stare at it for a minute. The manual dump valve closest to the waste tank must be open. The air powered valve must be closed. Just as Micheal said. That allows black water and grey water to accumulate in the waste tank. The accumulated waste drains when you open the air operated valve.

The plumbing is somewhat hidden in that it is hard to see that ALL grey water enters the waste tank from the tee fitting on the downstream side of the manual dump valve. All black water flows directly into the waste tank.

You can arrange the valves to permit gray water (shower) to bypass the waste tank. Close the manual valve closest to the tank, and leave the air operated valve open. All grey water will drain constantly, and all black water is now held in the tank. .