Sometimes before departure it happens that all the toilet flush systems become inop. The reason for the snag was found to be because of improper servicing of the waste system. After servicing of waste system it must be ensured that the ball valve be closed properly else the drain valve proximity switch will sense door open and disconnects the ground to the control relay of Vacuum blower thereby making the flush systems inop. Update: Another similar tip: THERE IS A COMMON PROBLEM OF ALL THE LAVS NOT WORKING WHEN THE A/C IS ON GROUND & READY FOR DEPARTURE. THE FIRST STEP IS TO CHECK THE CB ON P 18 PANEL & ON P 91. IF THE CB ARE IN, THE DRAIN BALL VALVE MECHANISM INSIDE TOILET SERVICE PANEL MUST BE CHECKED FOR PROPER SEATING. IF IT IS SLIGHTLY OUT THE PROXIMITY SENSOR INSIDE WILL SENSE AN OPEN CIRCUIT & NONE OF THE LAV SUCTION WILL WORK.