So yesterday we went and bought a Fleetwood hardwall, 2008, with a gray tank. The previous owners usually used hookups but said that once they didn't and learned that the gray tank apparently has an overflow on the outside. I don't know much about RV plumbing but it seems to me that that is probably not an "overflow" but maybe a vent or a regular old leak. Anyone know? We will try to mess with it today and see what's going on but darn that's a low trailer. I want a head start with information before I try slinking around under there... Thanks.