Mollie wrote:
As I said, it's a 35' sailboat with 11.5' beam....The holding tank is on
the port side. The tank is a heavy plastic one, rectangular in shape
and looks to be about 10-12" deep (est.)...

Where is the tank located, Mollie? On some 35.5 Beneateaus, it's just
aft of the head, in the port lazarette at the forward end of the
cockpit. If that's where yours is, the vent thru-hull should be right
next the tank and the line should go straight to it, using an elbow
fitting on the tank. That would give you a straight vent line less than
2' long. From your description it even sounds like that's actually
where the thru-hull is...but the vent line takes a "tour of the boat" to
get from the tank to it. So you may only need to replace your current
line with one that goes directly to the current thru-hull in straight
line to solve your problem.

If that's not where the tank is, it shouldn't be too hard for you to
figure out where a new thru-hull has to go to give you a short straight
line from the tank to it.


The current vent tube exits
the holding tank on the aft end. The vent tubing goes aft further
about 18" to just aft of the quarter berth. Before exiting into the
lazarette it actually goes down a few inches.

That's a problem...'cuz any sag in the vent line is a place where water
or waste can pool and block the vent.

It exits into the
lazarette and makes a fairly hard turn and goes up the inside of the
hull to the thru-hull that is just below the toe rail. Thinking
through the actual routing of this tubing, I imagine there is a strong
possibility that the blockage could be at the turn into the lazarette
being that it has the combination of being the lowest point in the
line and at the same time being the location of the sharpest turn in
the line.

That's a good possibility. Water can create a barrier, but it can be
blown out...but any waste will harden and build up till makes real
"plug" in the line. You don't want ANY low spots in a holding tank vent
line.

It released the
built up pressure from the tank quickly when I took the vent tube off
the holding tank.

You're lucky it didn't spray waste all over everything including you!

Never disconnect a hose if you suspect a blocked vent/pressurized tank
until AFTER you've relieved any pressure by loosening the deck pumpout
cap. Have a hose at the ready...'cuz if the tank is pressurized, waste
as well as air can start to ooze out as soon as the cap is loose enough
to allow to escape. And hang on tight to the cap, 'cuz if the tank is
seriously pressurized, the pressure can spin it the rest of the way off
once it's loosened a little. Loosening the cap is also the easiest way
to confirm that vent IS blocked.

(Another clue, btw, is any hissing sound in the head as the tank is
being pumped out...that's a sign that the vent isn't supplying enough
air--that air is being pulled into the tank through any other source
available).

I also verified that the vent was clear going back
into the holding tank when I removed the vent tube. I used a
screwdriver and there was nothing there.

Check the thru-hull too...that's the most common place for a tank vent
blockage. You could even have two--one in the low spot in the hose and
one there.

Meanwhile, don't try to pump out till you have an open vent (even if
that's just the fitting on the tank with no hose attached)...'cuz a
pumpout pulling against a blocked vent can crack a tank.

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://69.20.93.241/store/customer/p...40&cat=&page=1