Hello,

New construction, zone 6, coastal Maine, 1000 sq. ft..  I am about to break ground and am considering what needs to be done after my grade beams are poured and I am ready to start filling my sandbox.  I am a contractor, not a plumber.

The grade beams are 1 foot wide, so are the double stud walls above.  Its a non traditional system.  Setting aside supply questions here, only approach and drains, or anything else that needs to be considered before I fill the box with sand.  There is a self contained composting toilet that is not a part of the system.

All plumbing fixtures are on an exterior wall and run in a straight line.  In order, they go: bathtub, bathroom sink, washer, kitchen sink.   At the end of the run is my utility room where my grey water pump will be.  It pumps, through 2 inch line, under the subfloor to the other side of the building, where it exits the grade beam and continues to the drain field (8 elgins, etc.).

Here’s my plan.  I am going to put my grey water pump (probably a saniflo) into a plastic garbage can, surround it with insulation, and place it at an elevation in my utility room so that my main drain run can be easily plumbed into it.  Since there is no toilet on the system, i figure I can use 2 inch drain pipe for all fixtures.  I will have a main 2 inch pipe that runs horizontally (pitched 1/4 inch per foot) from the bathtub to the grey water pump and I will simply tie all of my fixtures into it.  The main would run just inside the grade beams about 6 inches below the subfloor and would stack vertically with the plumbing above. This would mean that my plumbing drains would be interior of my drywall (double stud walls) and would be concealed behind cabinets and closets which run the whole way.

I am told that I can use an AAV rather than vent each fixture.  The grey water pump has a through the roof vent on it, and i am hoping this is enough.

Thanks for any feedback or caveats.

Stephen