Install a y-valve in the pumpout line
One side of the wye goes to the deck fitting, the other side goes to the macerator and over a vented loop that's at least a foot above the waterline at any angle of heel to the thru-hull. Keep the thru-hull closed except when dumping the tank at sea. And keep the y-valve set in the pump-out position except when dumping the tank too. Just remember to switch it as necessary. The y-valve should be as cclose to the tank as possible and should be at the same level or below the tank discharge fitting. The macerator should also be at or below the level of the tank discharge fitting. Reason: to keep the impeller in the macerator from running dry more than a couple of seconds...running dry "fries" impellers. Now that I've told you how to do it, I need to tell you one more thing: what you want to do is illegal in the Chesapeake Bay. it's illegal to dump a tank within 3 miles of the nearest point on the U.S. coastline. That means 3 miles out to sea, not just 3 miles from the nearest shore--which means you have a long way to go from Rock Hall before you can legally dump your tank,
