I recently purchased a 72/ 38' HATTERAS. It has an onboard waste system for disposal at sea, but I want to pump it out at the dock. there is a Y valve off the tank, but everyone I talk to says to find out if I can pump before turning the valve. I can't locate a Hatteras owner in the area and the broker is clueless. The previous owner is out of the country for a month. any suggestions?