[Daryles]

I also have the Valterra gate valve. I put a 3" clamp around the connector end to prevent it accidentally falling off going down the road.

Hblick48,
It would depend on how your tanks are configured in your rig if this trick of sharing tank space would work.
I have a 3130re. The galley tank is mounted higher in elevation than the bathroom grey or black tanks. Therefore my galley tank will always drain into my grey or black tanks (I do the grey tank backflush trick too).
However, the 3" drain pipe between the tanks to the gate valve will hold about 8 gallons giving you some extra boondocking space for grey water. I wouldn't do it with the black tank.