When hooked up to the sewer connection at a camp sight, should I have both grey and black drain valves open?
The only time gray should be open is IF you have a washing machine during drain/rinse cycles so as to overfill the gray tank.
The only time black should be open is IF you have a black tank flush and are using it, so as to not overfill the black tank and its contents fill up the vent pipe and have its contents run off onto your roof.
