Most OEM's have a CYA warning about using the Washer. Usually it states to make sure the Gray Valve is OPEN when doing the Laundry. As long as you make sure the Gray tank is empty, then in transit should not be a problem. BUT, NOT COMMON, but there are some OEM's that do NOT plumb the Washer to the gray tank. It is plumbed straight to the outlet dump "Y"(really 3 inlet fittings). Usually those RV's will have a very prominent sticker stating this and you must have the Cap and Dump hose connected to the CG system. Have not seen this type in the past years, but was common years ago on some models. They did this because where the washer was located, they could not plumb it to the Tanks. Doug