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?

Thanks!

Crooked River