Roger Long wrote:
One of the things I'm not looking forward to about sailing is head
odor, especially in a boat where we'll be sleeping on top of the
holding tank.

If you're concerned about odor in the toilet, whether you sleep on top
of the holding tank has nothing to do with it...that odor is in the
head, not the tank...and odor from inside the tank--unless the tank is
leaking--only has one place to go: out the tank vent.

I'm thinking of setting up an arrangement like this:

I'll put a tee with a valve into the head intake line just upstream
from the seacock.

There's a much easier way. Tee the head sink drain into the head intake
line. To flush the sea water out of the head intake line--the whole
syststm, in fact--close the head intake seacock...fill the sink with
clean fresh water...flush the toilet. Because the seacock is closed, the
toilet will pull the water out of the sink. In fact, if you have the
fresh water to spare, you could just keep the intake seacock closed and
use this method to flush the toilet all the time.

--
Peggie
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Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://www.seaworthy.com/store/custo...0&cat=6&page=1