1 of the Mods Dad had me do to his 5th was put another drain in gray tank about 3/4 up. Line to 2 valves. Open 1, GW would tie back in to leave thru stinky-slinky. Open other, water can go out thru hose bib, directed into bucket, or where allowed, into bushes.
If tank is near full, the first water out when value opened will be fairly clean, if you need to flush something, or make sure your campfire is out.
As for the reduce water use; Wash dishes in pan, catch rinse water in another. The wash pan, dump down toilet to black tank. (Allow reduction in clean water needed to move the poop) The rinse water, should only have some soap in it. Next time do dishes, add hot water, use to wash.
As a side benefit, if that dish water, with any food particles, is stored in black tank, water that backs into shower floor will be lighter shade of grey.
