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Old 06-16-2010, 03:37 AM   #1
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Black Water Tank Vent

I have a Letrasan on my boat however i need to fit a holding tank also for the black water

The problem I am having is deciding how and what to do with the holding tank vent

Do you vent into the engine room or outside ??

Do you use a vented loop for the overboard discharge??

Through the hull or on the deck??

What do others have for their vents??

Allan

-- Edited by AllanY on Wednesday 16th of June 2010 05:41:49 AM
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Old 06-16-2010, 03:44 AM   #2
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RE: Black Water Tank Vent

Allan,
Go high if you can but away from where it may upset SWMBO or others.
On my own vessel it goes straight out the side via a thru hull.
Main thing is to ensure it is big enough to fully vent the tank and let good air in.

Benn
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Old 06-16-2010, 03:58 AM   #3
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RE: Black Water Tank Vent

We simply drilled a small hole in the pump out deck plate.

The flush rate is rather slow with out hand pumped toilet , so no problems in a couple of years,
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Old 06-16-2010, 07:18 AM   #4
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RE: Black Water Tank Vent

The key to not having odor is ventilation, a small hole in a deck fill is not going to allow any real air flow.
You dont want to have someone flush the head and have people outside gagging from the smell coming out of the vent.
The previous owners of my boat had a new holding tank put in by Maritime Sanitation the local so called experts on marine plumbing in the area. Over $6000 for the holding tank, VacuFlush, parts and labor and the installation work was horrible.
The 40 gallon tank had a 1 inch vent but the installer used a inch hose instead of 1 inch. You could always smell the holding tank outside when someone flushed. *I changed the hose to a 1 inch and added a 1.5 inch vent to the other side of the boat.* The holding tank odor is now gone.
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Old 06-16-2010, 07:39 AM   #5
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RE: Black Water Tank Vent

2 - 1.5" vents, one on each side of the boat is perfect. That being said, the more venting you have the better. I have one 1" and it is OK, but doing it again I'd have the above mentioned setup. Just straight mushroom vents through the side of the hull. Gotta vent outside! You should have a vented loop for overboard discharge; I put a hose barb in the "vent" part of mine and ran a tube through the hull to the outside as well.
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Old 06-16-2010, 07:56 AM   #6
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RE: Black Water Tank Vent

My holding tank had a 3/4" vent hose with a mostly clogged fuel vent style thru-hull.* When the head was flushed the smell was enough to gag a maggot.* This year I replaced it with a 1.5" hose & an unclogged mushroom thru-hull.* Flushed the tank, added some KO to get the aerobic bacteria going and so far, so good. But I would like to run another vent through the other side of the hull to ensure cross ventilation.
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Old 06-16-2010, 01:41 PM   #7
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RE: Black Water Tank Vent

And what about a screen on the vent? During the course of unplugging our holding tank vent line last summer we bored right through the screen (located at the hull fitting). Any advice I've received since has been very contradictory, so to date we have not replaced it.
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Old 06-16-2010, 08:27 PM   #8
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RE: Black Water Tank Vent

We vented ours up to the top of the mast.** Most trawlers don't have that option, so the next best, IMHO, is a vent below the waterline, as long as an anti-siphon loop with the top of the loop 3 feet above the waterline is possible.* Some don't like the bubbling every time the head is flushed, but the odor is significantly reduced with this setup so you have to decide if slightly smelly bubbles are less obnoxious than really smelly eau de septic tank.

Another alternative is to install a bubbler that blows air into the holding tank.* This pretty much kills the odor and you can then vent it whereever is most convenient.

A definite 'no' on E/R venting, or through the deck.
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Old 06-16-2010, 08:55 PM   #9
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RE: Black Water Tank Vent

Cross ventilation as high as possible with the largest line possible. Two vents will allow cross ventilation which will allow the microbes to do their thing which will eliminate odors. I've never seen an installation from a manufacturer yet that is adequate.
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Old 06-16-2010, 09:32 PM   #10
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RE: Black Water Tank Vent

Don't forget I have a Lectrasan treatment system on board so the smell is not that bad
The holding tank is for the marina and areas within the national park

Allan
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