how to install head?
Sorry, I was being facetious about the “difficulty” in drilling holes through your hull when afloat - it’s just NOT practicable.
I neglected to indicate Holding Tank Vent lines on my CruisersForum plumbing diagram.
Holding Tank Vents:
The Sewage Holding Tank requires Venting, to allow for proper ventilation (eliminates odours) and to avoid creating a vacuum when pumping out. I recommend TWO Vent lines, promoting cross-ventilation.
Vent lines should connect to the top (not sides) of the Holding Tank, and continuously slope slightly upwards to the Vent Caps, which are installed as high as practicable on opposite sides of the hull. The Vent hoses should be at least 3/4" diameter (larger is better), and as short (direct path) as possible.