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Old 09-25-2016, 08:05 PM   #4
HeadMistress
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City: AR
Join Date: Jul 2009
Posts: 2,515
I only had to read the first few sentences to be 99% certain that the "man they sent down" checked every line but one: the tank vent. I'd bet real money that your problem isn't in the tank, it's a blocked vent.

A tank vent--any tank, fuel, water or waste--has two main functions: it provides an escape for air displaced by incoming contents and provides a source of air to replace contents as they're drawn out.

When no air can escape as new contents are added, the tank can become pressurized. Fortunately your boat sat long enough for any pressure in the tank to dissipate or you'd have been "baptised" by geyser when you opened the deck pumpout cap. When no air can be drawn in as contents are pulled out, the pump will pull a vacuum that will only let a small amount be pumped out before the pumpout or macerator pump pulls a vaccum that prevents it from removing any more. A particularly strong pumpout pulling against a blocked vent can implode a tank.

The most common locations for a holding tank vent blockage are 1) the vent thru-hull, 2)the other end of the vent line--that end of the hose and the vent fitting on the tank...and 3) a filter in the vent line. If you haven't overfilled the tank, causing it to overflow out the vent, we can prob'ly rule out the filter--they only block the vent if they get wet. That also reduces the odds of a blockage anywhere BUT the vent thru-hull. Clean it out with a screw driver blade, ice pick or whatever works. If there's a screen in it, knock it out...screens cause more problems than prevent or solve. That should solve your problem.

If you want to prevent this from happening again, replace the "vent" thru-hull that all boat builders use on every tank vent with an open "bulkhead" or "mushroom" thru-hull that you can put a hose nozzle up against and backflush the vent line every time you wash the boat.

Peggie
http://www.amazon.com/New-Get-Rid-Bo...dp/1892399784/
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein
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© 2024 Peggie Hall
Specializing in marine sanitation since '87.
Author "The NEW Get Rid of Boat Odors"
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