[bobbecky]

Our rig is obviously different from yours, but our black and grey tanks are mounted along side each other and out of the rear of each tank is a drain valve. From each drain valve is a 90 degree elbow turning toward each other and meets up with a wye fitting where the two lines connect to and from the wye fitting the three inch line exits the belly area and turns toward the left side of the rig. Our galley tank is mounted aft of the axles and the two inch line from that tank connects to that three inch line going to the left side of the rig. We don't have a washer installed, but that line connects to the three inch line after the two tanks, black and grey so if draining requires no valve operation so must be connected to a drain directly. Hope this helps.