OWTW now has a vented loop between the head pump and bowl. I did a
quick "proof of concept" check by hanging a hunk of 3/4" hose off the
pump intake barb and another off the bowl inlet barb and stuffed the
vented loop in between. Not too surprisingly, the bowl filled as it
should and no siphoning was seen. However, after I stopped pumping, the
residual water in the hose downstream from the vent did empty into the
bowl (it looks like siphoning but does stop). I then set about putting
the loop out of site, inside the vanity, next to the toilet. The space
behind the toilet was not an option as there is a stretch where running
any hose, let alone 3/4" (ID) hose, is out. The sole option was the
vanity cabinetry, under the sink. The keep the extra hoses as
unobtrusive as possible, I used 3/4" white sanitation hose and a white
elbow for the turn from the pump intake barb to the cabinet. I drilled
two 1" diameter holes (the hose is something like 15/16" OD) and passed
the hoses into the cabinet, inserted two elbows, and two 12" risers
leading to the vented loop. Clamped into place, everything worked as
expected; I screwed the vented loop in place and that was the end of the
plumbing work. "All" that was left was cutting notches, in the
removable shelf bottom, for the hoses, doing a little "cut and fit", and
then wiping calk around the hoses to limit water getting into the
cabinet from the head (and shower). Probably the single hardest part of
the job was getting the sanitation hose over the various barbs. Even
some vigorous use of a hair drier could only do so much.

It's useful to know the location of the waterline relative to the
interior of the boat. I stuck a piece of clear hose onto the raw water
inlet seacock, pulled it upright, and cracked open the valve. Water
rose to a point and stopped - at the waterline. The vented loop is
about 9-10" above this point and should be above the waterline even when
heeling hard on port tack.

Cheers,
Rick

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Received on Sun Jun 3 19:01:50 2007