fleetwood grey water drain problems

I don't understand it either, grey water tank is mty, I put a garden hose down the vent and water ran out of the gate valve drain so the vent is clear. It is plumbed the same as a house sink drain plumbed with a vent stack. The water to drain is 1/2 tub of one side of a double sink. Seems if the water will not let air go up the stack. I even instead of plugging the stopper right out, just only lifted a bit but did the same thing. Quess it is a good question for a Fleetwood factory rep.

The shower drain is much higher than the gray tank drain valve. I agree, unless the tank is full, I don't see how in the world the water can back up to the shoer drain. Doesn't make sense.....even with the roof vent clogged and not allowing any air to escape. The air in the tank (if empty) would definitely push air up the shower drain as the water flowing into the tank displaces it, but I just don't see how the water could do that. Got me stumped.

Ron

Maybe you have a gray water tank vent problem. When you checked the roof vents, are you sure the tank is actually venting? If the vent is plugged, when water from the sink enters the tank, it vents through the shower drain - pushing liquid from the P-trap into the shower pan.

Need more information , as to volumes of water draining, what valve you are opening and closing, as no logical conclusion can be drawn from an empty tank allowing water into shower, only full tank overflowing would do that.