Anybody with a 318SAB. Looking at this one, it has 76 gal gray, 38 waste but only two tank handles, are the two gray tanks connected to one drain? (Assume there are two)
IF it has 2 grey tanks (grey waste and a 'galley'----kitchen sink) then the galley one should have its own drain handle.....typically back behind/between trailer wheels.
The galley may have its own drain line requiring a hose hooked up OR it could tie into main drain header.
My 5vr has black, grey & galley and fortunately all come out a common drain header so only one hose hook up needed