Utilizing ideas from this site. Does anyone see any problems with having all waste go to tank then being able to pump overboard thru seacock or normal deck pump out.
The high point vent is to let air
IN. The tank vent is to let air
IN and
OUT.
They serve different purposes. Making the vents a closed loop will not work.
The size of the tank vent
IN is done by the outflow of liquid by the Macerator pump/dock pump.
Simple view is that 5 gpm black water out... you need 5 GPM of air flow
INTO the hold tank to balance tank pressure.
The head pump to the hold tank is normally so much smaller flow, it is not controlling pressure vent sizing.
The high point siphon break is only needed to prevent back flow of sea or hold tank (depending on how you pipe it) to head.
My high point is on the Head pump and not the macerator pump. You will pump black water into boat if the siphon break fails.
Tip: To stop any siphon with out the vent, close your exit valve/seacock and wait a few minutes. Siphoning is a dynamic or moving thing. No flow... no siphon!
Jim...
PS: Your tank vent though hull should always be AWL, even when heeled over. I back flush my 3/4" tank vent twice a year with shore water hose to confirm no insect blockage. Its location should not be near the cockpit when someone uses the head peweeeeehhhh.:cussing: