A blocked vent will pressurize the tank--the whole system in fact, creating back pressure when you flush that won't let bowl contents go anywhere or will start causing the toilet to burp and/or gurgle when you flush....your first clue.
While not impossible,a blockage in the vent LINE isn't common...the exception can be a spider nest in it. The two most common locations for a vent blockage are the vent thru-hull and the other end of the vent line--that end of the hose and the vent fitting on the tank. Start by cleaning out the thru-hull...use a screwdriver blade, ice pick--whatever works. Better yet, just replace the "vent" thru-hull with the open bulkhead fitting I described above. (If the blockage is in the thru-hull, be prepared for a spew out the side of the boat when it comes out.)
If that doesn't result in a spew out the vent, you'll need to relieve the pressure before removing the vent line from the tank to clean them out...so open the deck pumpout fitting VERY CAREFULLY with a hose at the ready. Be sure you're UPwind of it! Scrape out that end of the vent line and the vent fitting on the tank...reconnect the vent line.
If there's a filter in the vent line, remove it...once a filter gets wet--which can happen when a tank is overfilled or even due to heeling--the charcoal swells and blocks the vent.
As with most things, prevention is easier and often a lot cheaper than cure. An open vent thru-hull that allows the vent line to be back flushed by putting a hose nozzle against it is cheap and easy blockage prevention.
--Peggie
While not impossible,a blockage in the vent LINE isn't common...the exception can be a spider nest in it. The two most common locations for a vent blockage are the vent thru-hull and the other end of the vent line--that end of the hose and the vent fitting on the tank. Start by cleaning out the thru-hull...use a screwdriver blade, ice pick--whatever works. Better yet, just replace the "vent" thru-hull with the open bulkhead fitting I described above. (If the blockage is in the thru-hull, be prepared for a spew out the side of the boat when it comes out.)
If that doesn't result in a spew out the vent, you'll need to relieve the pressure before removing the vent line from the tank to clean them out...so open the deck pumpout fitting VERY CAREFULLY with a hose at the ready. Be sure you're UPwind of it! Scrape out that end of the vent line and the vent fitting on the tank...reconnect the vent line.
If there's a filter in the vent line, remove it...once a filter gets wet--which can happen when a tank is overfilled or even due to heeling--the charcoal swells and blocks the vent.
As with most things, prevention is easier and often a lot cheaper than cure. An open vent thru-hull that allows the vent line to be back flushed by putting a hose nozzle against it is cheap and easy blockage prevention.
--Peggie
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