Turn Key wrote:
You can but I wouldn't. Sludge will build up and dry in the bottom of the tank causing issues down the road. Better to let the grey water fill the tank and then drain it every few days. Will keep the sludge moist and allow it to drain away with the water. Your call, though.
Happy Camping!
^^^ THIS ^^^
To a lesser extent, soap scum and some food particles can build up in the tank. (although we wipe away all food particles prior to washing) As with the black tank, emptying large volume all at once helps to drain most of that out of the tank.
Letting water just flow out often leaves soap scum and food particles behind to dry out.