[Fulltiming]

Steve is correct. Grey water is routed into a single pipe that dumps into the line coming from the waste holding tank to the sewer connection on the driver's side. There is a valve on each side of the grey water line. If the valve between the grey water line and the tank is closed and the valve closest to the sewer hose connection is open, all grey water will drain through the sewer hose and all black water will be trapped in the waste holding tank. This is the normal position when you are parked with sewer hookups. Closing the valve closest to the sewer hose and opening the valve on the other side of the grey water line will let all black and grey water go into the waste tank. This is typically used when driving or when parked without a sewer connection. Opening both valves will allow all waste and grey water to flow out of into the sewer hose.

The connection on the passenger side dumps the contents of the waste tank. I have used that connection when, due to a view at the rear of the space, I headed into a space that was designed to be backed into. That was the sewer hose had a short run to the park's sewer connection. It is not possible to dump just grey water from the passenger's side dump valve.

It is not possible to 'store' grey water separately. After dumping the waste tank, you can close the valve between the grey water line and the waste tank, turn on a faucet in the coach and flow clean water through the sewer hose. Attempting to store grey water separately will typically end up with a shower full of grey water (the lowest grey water drain inside).