Crooked River wrote:
During the past week the friction-fit green vinyl cap of the NozAll
adapter on our holding tank pump-out has popped off on its own --
twice while under way and once while sitting at the dock on a warm
day. Apparently gas pressure is building up in the holding tank, and
the vent must be plugged, so it pops the cap.

I've seen advice in this forum to clean out the vent using a water
hose, but there are a dozen thru-hull openings, and I don't want to go
shooting water into the wrong one. (I bought the boat last fall but
just started using it.)

Can anyone tell me where is holding tank vent thru-hull on 1989 Carver
28 ft. Montego?

It could be anywhere depending on whether the tank was factory installed
or owner installed...so you'll have to find it. Start at the tank and
trace the vent line to the hull.

You're lucky that only the cap pops off (why are you leaving the pumpout
adapter attached to the pumpout fitting? That's a good way to lose it.)
'cuz a blocked vent can easily result in a cracked tank or eruption in
the toilet. Don't use the toilet again or attempt to pump out the tank
until you've cleared the vent. Keep the vent clear in the future...never
allow the tank to over flow...backflush it with water after every
pumpout and each time you wash the boat.

And put the pumpout adapter away and get a proper threaded cap for your
deck pumpout fitting.

--
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