I have a Catalina 350 with an electric head that pumps waist behind the head into a holding tank. The tank is 25 gallons and empties through a gravity dump. I think it's a 1.25" line. Well it seems to fill awful quick and does not empty correctly. When I turn the valve to dump there is a quick release but a vacuum seems to form and won't drain the tank completely. I ended up opening up the topside pump out and broke the vacuum and the waist released. So there are a few problems. On the way back from the islands I went to open the top side pump out plate and waste started coming out, which forced me to open the gravity valve first. I don't think it was full but I don't have a tank gauge. It worked but shouldn't the antiphon hose in the cabinet break any vacuum in the tank? How much water is the head generating during a minor flush?
2002 Catalina 350 holding tank
- Thread starter bertram
- Start date
Your problem is a blocked tank vent....and no, the vented loop won't break a vacuum in the tank. All tanks vents--fuel, water and waste--have two primary functions: to provide an escape for air displaced by incoming contents and to provide a source of air to replace contents as they're drawn out. When a holding tank vent becomes blocked, continuing to flush the toilet pressurizes the tank...which explains why waste gushed out of the pumpout fitting when you opened the cap. When no air can enter the tank to replace contents as they're pulled out, the pump--pumpout or overboard discharge pump--will pull a vacuum that prevents more than a small amount from being pulled out....which explains why neither pumpout nor your gravity drain could empty the tank. Clearing the vent will solve your problem. Do NOT use the toilet again until you have cleared it.
The two most common locations for a vent blockage are the vent thru-hull--which on a Catalina is only a slit in a rail stanchion unless a PO has relocated it to a thru-hull-- and the other end of the vent line--that end of the hose and the vent fitting on the tank. Start by scraping out the slit in the rail stanchion or the thru-hull if there is one...use a screwdriver blade or whatever works. Then remove the vent line from the tank (warming the hose a bit with a blow dryer will make it easier to get off)...now that you've relieved the pressure by opening the pumpout cap, it should be safe to do so without spewing waste all over that area, but I'd open the cap again before you remove the hose just to be on the safe side. Scrape out the end of the hose and the tank fitting. Put em back together and you should be good to pumpout.
There's an ongoing discussion about this in the Plumbing and Sanitation forum and in at least one of the Catalina forums now...you might want to check them out. And the archives of the Plumbing and Sanitation and the Ask All Sailors forum are full of blocked vent threads. Spending a little time reading them will help you prevent a lot of sanitation system problems.
The two most common locations for a vent blockage are the vent thru-hull--which on a Catalina is only a slit in a rail stanchion unless a PO has relocated it to a thru-hull-- and the other end of the vent line--that end of the hose and the vent fitting on the tank. Start by scraping out the slit in the rail stanchion or the thru-hull if there is one...use a screwdriver blade or whatever works. Then remove the vent line from the tank (warming the hose a bit with a blow dryer will make it easier to get off)...now that you've relieved the pressure by opening the pumpout cap, it should be safe to do so without spewing waste all over that area, but I'd open the cap again before you remove the hose just to be on the safe side. Scrape out the end of the hose and the tank fitting. Put em back together and you should be good to pumpout.
There's an ongoing discussion about this in the Plumbing and Sanitation forum and in at least one of the Catalina forums now...you might want to check them out. And the archives of the Plumbing and Sanitation and the Ask All Sailors forum are full of blocked vent threads. Spending a little time reading them will help you prevent a lot of sanitation system problems.