That may allow you to completely eliminate the vented loop in the system. I know it did on my head. The picture below shows my head setup. The waste goes into the holding tank at the left. The outlet for the tank is top right (there is a pickup tube that extends to within 1/4" of the bottom of the tank. From the tank outlet the hose goes to a Y-valve the lets you choose either the deck pumpout or the overboard discharge via the whale pump on the bulkhead. The seacock is closed unless you are pumping overboard. In my setup, the bottom of the tank is above the waterline. The system is only connected to seawater when the pumpout seacock is open. The inlet to the head is plumbed to the head sink drain. Consequently, we use fresh water to flush. We just run the amount of water we want to flush with into the sink. That allows us to easily control how much water goes into the head and makes the holding tank last longer