Below Waterline - Head installation and Vented Loops

[Apex]

If I am reading and interpreting correctly, I only need ONE (1) vented loop:
Vented Loop between bowl and pump.

I have a below waterline head, and holding tank ONLY, no option for overboard. Looking at Peggie's book, and the Raritan PHII, the vented loop for discharge from pump is only IF OPTION exists for having connection between the sea and head discharge, either directly plumbed to an outlet seacock or through a y-valve to an outlet seacock.

Finally getting close to completion of the holding tank upgrade. 25gal AND it is mounted in the bow, resulting in regaining the below bunk shelving and footwell in the V-berth that a P.O. utilized for an improperly installed and improperly vented holding tank. :O)

 

[Don S/V ILLusion]

i can’t imagine any cause for backfliw from the tank into the head. How much do you heel?

 

[RoyS]

Suggest you consider installing an inline filter for your raw water intake before the pump. Sea grass can foul your pump and the filter will prevent that. Groco makes a nice one.

 

[dlochner]

If I am reading and interpreting correctly, I only need ONE (1) vented loop:
Vented Loop between bowl and pump.

I have a below waterline head, and holding tank ONLY, no option for overboard. Looking at Peggie's book, and the Raritan PHII, the vented loop for discharge from pump is only IF OPTION exists for having connection between the sea and head discharge, either directly plumbed to an outlet seacock or through a y-valve to an outlet seacock.

Finally getting close to completion of the holding tank upgrade. 25gal AND it is mounted in the bow, resulting in regaining the below bunk shelving and footwell in the V-berth that a P.O. utilized for an improperly installed and improperly vented holding tank. :O)

That is correct. The vented loop must be above the waterline at all angles of heel. The easy way to find that location is put the loop well inboard and at or above the height of the side deck.

From the bowl to the holding tank there needs to be a loop that goes higher than the holding tank. The main reason is to reduce the amount of pumping necessary to get stuff to the tank, let gravity do the work. In some installations the inlet for the holding tank could be above the bowl, thus when the tank is very full some contents could run back into the pump.