SV Pilgrim - 1979 Morgan 382 - Homeport: Beaufort, NC

Tuesday, September 30, 2014

Holding Tank and Blackwater Plumbing Complete

The new holding tank and blackwater plumbing system are installed and tested.  The system has gone through quite an evolution.  I posted my initial concept here on the website and on the Morgan 38 Discussion Board.
The original schematic for Pilgrim's blackwater plumbing

Thanks to comments, questions, and feedback from you all, I made a few modifications prior to beginning the project.   Once completed the initial installation looked like this…
The actual layout of the initial installation.

Since Pilgrim is on the hard testing the system required routing the head raw water feed line to a 5G bucket of water.  This plumbing detour allowed me to flush the toilet both overboard and into the holding tank.  The system worked flawlessly during this test. For the next test I filled the holding tank with fresh water via the pump out fitting on deck.   While watching the tank fill, I realized a shortcoming of the design – the Henderson MKV Pump was mounted lower than the holding tank.  With the valve at the tank exit set to offshore discharge the Henderson  Pump the pump would flood.  I questioned whether or not the flapper and joker valves in the pump would operate properly with constant positive pressure from the holding tank.   The Henderson Pump performed the task of empting the tank without issue, but...  my design would leave the valves of the pump submerged in black water anytime the tank exit valve were open to the pump.  I feel certain that prolonged immersion in black water would cause the valves to fail unless they were regularly cleaned.   Monthly or weekly cleaning of the head pump internal valves is not a task I want on my regular maintenance list!

The next (dare I say final?) evolution…
The current, and I believe final, installation of Pilgrim's black water system

Despite my resistance to adding another electric pump to the vessel, mounting the Shurflo 3200 Macerator below the level of the black water tank is within its design specs.  I also inverted the “Y” valve in the offshore discharge line.  Flipping the valve allows all the waste in the line to empty past the valve.  In the previous design a small amount of black water remained in the valve after use.

Using the same methods as above… 5G bucket of water plumbed to the toilet feed line and filling the holding tank via the deck pumpout fitting, I have successfully tested all the functions of this system.

Flushing head offshore the waste follows the path highlighted in red.
Flushing to holding tank the waste follows the path highlighted in red.
Discharging the holding tank via the deck pump out fitting the waste follows the path highlighted in red.
Discharging the holding tank offshore the waste follows the path highlighted in red.
Additional images and notes from the installation can be found in our on line Holding Tank Installation Photo Album - 2014


  1. Does the final installation of your head and macerator pump include two (2) vented loops? It looks like you have one (in the diagram) just after the outlet of the pump, but the depiction in the drawing is a little different than the other vented loop in the drawing.

    1. The final assembly has two vented loops. One between the head pump and the thru hull seacock (when flushing head directly overboard) and one between the macerator pump and the thru hull seacock (when emptying the holding tank overboard).