wrote:

I've been reading the old posts on this ng about the Sealand 965Msd and
the Traveler. They are attractive to me because they seem simple,
versatile, compact and are generally getting good reviews on this ng.
However, I haven't read a discussion of how (or whether) to vent these
holding tanks in a fixed (permanent or semi-permanent) installation.
Is venting advisable? Necessary? Should venting be accomplished via a
"Y" or "T" in the pumpout hose?

The SeaLand 711-M28 Traveler MUST be vented...You can read the
installation instructions he
http://www.sealandtechnology.com/pdf...0OM%203-02.pdf

The 965MSD and any other permanently installed "pumpable" portapotty
should also be vented...if not, pumping 'em out becomes a 2 person
job--one person to man the pumpout, another to keep the "trap door" in
the bottom of the bowl open so air can get in to replace the contents
being pumped out. Otherwise, the pumpout will pull a vacuum that
prevents it from pulling anything out of the tank.

You can't tee a vent line into the pumpout line, for a couple of
reasons...1. It wouldn't work--no source of air in the pumpout line, no
way for gasses to escape. 2. Because methane is flammable and hydrogen
sulfide and sulfur dioxide are toxic--even lethal in high enough
concentration--CG regs require that all waste tanks be vented to the
outside of the boat...so whether it's a remote tank or a tank in a self
contained system, the tanks MUST be vented the same way any other
permanently installed tank is vented: a separate vent line that comes
off the vent fitting on the tank that goes to an above waterline
thru-hull on the outside of the boat...same as a fuel tank.

The Traveler is a permanent installation that can only be emptied by
pumpout or dumped at sea...the tank cannot be carried off the boat.
Although you can disconnect the vent and pumpout lines from a
permanently installed portapotty to carry the tank off the boat, a full
5-6 gal portapotty tank weighs about 50 lbs...a LOT to carry off the
boat and haul up a dock--IF you can even find a marina that'll allow you
to dump it. Since you're unlikely to go through that hassle more than
once, it should also be considered a permanent installation.

--
Peggie
----------
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://shop.sailboatowners.com/books...ku=90&cat=1304