Have you noticed it takes a long time to ask a head question. Last July we noticed sewage dripping from the Head vent on our O'Day 272 at the pump out station. Eventully that morning we did get the head empty as the water line boot-stripe reappeared....Head worked great there-after....after labor day we went to another pump out station at our club and it never seemed like we got anything out, although I'm nearly certain it was full....no one has done anything in it but number 1...although I'm certain my wife uses marine toilet paper.....Anyway, again at the pump out we could not get it to really pump. Several other boats were also having trouble getting the pump out to work right so I didn't think much about it as I was relatively certain the holding tank was not totally full....so I poured antifreeze into it (approx. 3 gallons)....It seemed like it was unhappy pumping the raritan PH II head...I sent out side and noticed the vent was dripping again....I'm certain the head holding tank is either full...the vent clogged (boat is 24 years old)..what should be my first steps in solving this....should I blow out the vent hose if I can...??? help. Your thoughts and ideas are appreciated.