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?

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

Venting is neccessary to enable fuids to move into and out of tanks.
Vents also reduce odour, if efficient enough, allowing oxygen into the
mix, preventing anerobic reactions, which actually cause most of the
stink.

If you vent the pumpout hose, how will you maintain "suction" when
pumping out? A vent valve might work, but needs management, is all.
Imagine being at the fuel dock, ready to go except the pumpout isn't
working. One distraction and you could hold up the works because the
pumpout suction line vent is mysteriously open. Besides, the vent
won't breathe the tank if it is in the suction pump out line.

I don'tsee any benefit in the idea.

The tank vents are better connected directly to the top of the tank,
and should be roddable, to clear them as required.

I made my own perfectly fitted waste tank from leftover glass and poly
resin, using a stitched together, waxed wooden form that came apart
inside the finished tank, before forming a flange from bog to which was
sealed the top of the tank. I use a compressed air system to blow the
tank when dumping at sea, or into an external toilet hose connected to
a floating barrel for near shore self help pump outs, or to Wall Mart
parking lot storm drain or service plaza, as is so popular with the RV
crowd.

The only in line sewage valve is a plasic ball valve at the marine
discharge through hull. When closed ("port" position) toilet goes to
tank. When discharge valve is in the "sea" position, toilet waste goes
to the tank and sea until the tank level is even with the waterline,
unless to vents are closed, in which case, the system "goes" to the sea
once there is any overpressure pressure in the holding tank. So, I can
manage ballast as well as is done in a submarine. Usually, the through
hull is closed, as a matter of safety, and is only opened to empty the
holding tank if not using the on deck pump out fitting.

One or two pounds pressure is enough to purge the tank in two minutes
or less, and it is neccessary to have valves in the vent lines to
enable this operation. I use a cheap 12VDC tire pump to pressurize the
system for purging, and an RV air purge shraeder valve in the vent
line, between the vank and vent valve.

When purging, I observe any backwash from tank to toilet bowl, as a
method of monitering the condition of the duck bill, or "Joker" valve.
Any sign of leakage would be reason for maintenance. Opening either
vent valve immediately relieves pressure in the system.

Peggie doesn't like my plan, but I do.

Keep through hulls closed unless in use and monitered!

Terry K