Many trailers, 5th wheels included, will have 2 grey tanks, one for bathroom and one for kitchen depending on your floor plan. Our older 5th wheel had two valves one for each grey tank, first one with the blank flush and the second in the back at a separate hookup and drain. With our 2015 trailer there is still 2 grey tanks but it has a long pipe that connects it with the main drain so only one hose hookup but you still must walk towards the back and pull that grey tank separately. When I'm draining I just hook up the drain hose and start at the rear grey, the kitchen drain in ours, let it drain for a while, close it and move forward, drain the black then drain the bathroom drain since with the shower that's usually more water to flush out the residue of the black then the kitchen anyway. But yes as others have said, if you have a panel showing 2 greys, you've got 2 greys to drain!