Stainless steel deck pump out and vent. The pump out fitting requires a 1-3/4 hole, and the deck is plywood cored.

For the pump out fitting, I first drilled a 2 hole through the deck, but not through the inside liner. Then I re-inserted the plug and filled the space around the plug with Marinetex, then drilled a 1-3/4 hole all the way through the inside liner, so the wood core is sealed from moisture.

I also drilled oversized holes for the screws, filled with Marinetex, then re-drilled screw holes, sealing the wood core. The vent hole has no wood, and the rubber gasket provides a good seal.

The hoses are connected to the five gallon holding tank.

Using a MSD porta-pottie still allows manual dumping of the holding tank should a pump out facility not be available. I used a sink drain wall pipe from Home Depot to connect the large pump out hose. The small vent fitting is for a washing machine hose. I had to use the elbow connectors to make the turn I needed under the cabinet. Both are easily disconnected for manual dumping.

The hoses run up through the cabinet, and out the top. The cabinet does a good job of hiding the hoses.