We have a porta potty allowing for a pump-out connection. Installed an appropriate pump-out hose, an external suction fitting, and a vent. The hose of the vent line is overkill; a pressure hose is not needed, since this line is to allow air in to enable fluids to be sucked out from the porta-poty that only has a minuscule venting hole. The stainless steel pump-out fitting is installed through the deck, between the winch and the stanchion. All holes were overdrilled, core balsa (deck) scraped from edge, epoxied, and fittings cemented with 3M 5200. The picture showing the external air vent is from another boat, but I used exactly the same installation.