Simply to install. Minimal equipment requirements. Does not require a through hull for discharge. External pump required to evacuate tank. Overboard discharge option after the holding tank.
All sewage is pumped into the holding tank.
Boat will use pumpout facility in port. When beyond the three mile limit, untreated sewage can be pumped directly overboard. The deck pumpout fitting and the overboard through-hull valve are normally pressure tight and will function alternatively as selected. Overboard discharge options both before and after the holding tank. Flexibility is offset by complexity.