RV Repair: tub, grey water tank, waste tank

Question
Tub wont drain after shower unless I open valves and drain entire waste tank.

Answer
Is it possible that the tank got full?  I assume you mean the grey water tank.  A shower uses much water.  And if your tank is not real big, you could be full to capacity.  Another problem may be the vent.  The tub drain need to ventilate.  If your vent is plugged, it could cause the tub not to drain.