[Fulltiming]

The 1990's models have two drain valves in series. The one closest to the hose connection opens the grey water to the drain hose, the one inboard of that valve opens to waste water tank. If the waste water tank valve is closed and the main valve is open the grey water goes out the hose. If the waste water (tank) valve is closed mine has a diversion pipe that overflows into the waste tank. If yours does not have a diversion pipe and has the two valves, close the front valve, open the rear valve and the grey water will flow back into the waste tank.

If yours doesn't have a second valve, I am not sure what they did as I have never seen a Newell with a single waste tank and only one valve on the driver's side.