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Old 01-05-2015, 09:20   #1
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Another holding tank vent question

I'm almost sorry to bring this up again as there are many many threads all over the internet about this subject and i would hate to admit how much time i've spent reading on this subject and still don't really have an acceptable answer so i am going to ask.

Background, bought an Old PaceShip PY26 that had a big bladder for the black water holding tank that stank. I have replaced the entire system from head to hose to bladder. We felt we could not put a hard tank in so we got a Vetus bladder.

The old bladder was not vented and the new bladder has a 5/8 vent tube connector factory installed. So after all my reading I understand that venting the holding tank will hopefully reduce/prevent the stink.

However my big concern right now is where to place the through hull vent.I have purchase a standard stainless steel though hull vent with 2 screened holes almost side by side. Something like this Gas Tank Vent .63 Chrome Plt Thru Hull Fitting 5/8""H

The bladder is under a settee in the cabin right about in the middle of the boat as close to the head as possible. I feel like i want to mount the vent just below the rub rail in the middle of the boat so that my vent line is as short and straight as possible. However i am concerned about water getting sucked back down the vent line and filling the bladder when healed over on that side. I feel like with the 2 vent holes facing backward it may not be a problem. Maybe put a valve on the vent line to close while sailing and open when at anchor or docked or will a loop in the hose before the vent prevent this.

The other options is to place the vent above the deck but i think the smell from the vent would waft into the cockpit. I had someone say just run it back to the transom but this would require about 13 feet of 5/8 vent line,which may need to partially lower then the bladder itself, instead of about 3 feet straight up.

What the communities recommendations on this situation(other then switch to a solid holding tank) and thanks in advance.
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Old 01-05-2015, 11:54   #2
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Re: Another holding tank vent question

Your concerns are well founded.

Place the vent as high as you can off the water with the shortest hose length possible. Be sure to use oderloos in your holding tank and this will drastically cut down stink. YOu really should not notice much stink at all.

If you make the hose too long, you will not get the proper air flow.

Also, you may want to run two hoses - put a T fitting pretty much at the tank and then run one hose to starboard and one to port. When air is flowing from one side or the other it will further ventilate.
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Old 01-05-2015, 12:13   #3
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Re: Another holding tank vent question

It's the wrong vent.

Get a mushroom thru hull.

http://c34.org/bbs/index.php/topic,6861.15.html
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Old 01-05-2015, 15:20   #4
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Re: Another holding tank vent question

What stu says. A mushroom. Mount it as high as you can on the hull to keep the ocean out. I occasionally squirt some pure bleach into the mushroom and down the hose to kill anything that might want to grow in there.
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Old 01-05-2015, 17:25   #5
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Re: Another holding tank vent question

Our Cabo Rico uses the gas tank vent as well - I took out the screens.
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Old 01-05-2015, 17:48   #6
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Re: Another holding tank vent question

I recommend that you use a porta potty that includes a pumpout fitting...a bladder? Sounds like a horrible idea. Porta potty is cheap and air tight except when flushing. A 26' boat is too small for a proper head but can be fitted with a pump out fitting. Use the best chemicals and pump out often. Purge the tank with fresh water often. If it gets smelly, just get a new one. I did it for 20 years. Works reasonable well.
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Old 01-05-2015, 17:58   #7
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Re: Another holding tank vent question

Stu and Mark are right; you don't want a fitting with a screen in it.

However, a bladder is different from a tank in one important way, and thus I don't think we know the answer. A bladder is always full, in the sense that there is zero headspace.
  • That means that there will be zero air air flow into the tank under any circumstance. There is no head space and the liquid will always be up the vent a few inches (whatever static head the weight of the upper membrane contributes). CO2 and H2S, among other odoriferous gasses generated by anaerobic decomposition may escape, hopefully without burping blackwater with them. The bag will be prevented from over pressurizing.
  • Adding bleach is a bad idea. It won't be enough to sterilize the contents (I doubt the whole bottle would, as the biomass in the bottom would be shielded by the sludge layer, and the hypochlorous acid would soon be spent chewing on biomass). It will also be hard on the bag, increasing permeability (proven on hoses in lab testing and the real world--NO manufacturer recommends bleach.
I think the OP would be much better off finding a PE tank that fit the space. Ronco makes many. I would return the bladder if it has not been used. Failing that, run the vent as far as you like, since there will never be airflow; however, keep it high or the risk of bad plugs soars. But I would not return to a system you know will fail.
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Old 02-05-2015, 09:31   #8
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Re: Another holding tank vent question

The Head Mistress, Peggy Hall, is the expert. Most other advice stinks a bit.
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Old 02-05-2015, 09:48   #9
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Re: Another holding tank vent question

Quote:
Originally Posted by AlwaysFORSAIL View Post
The Head Mistress, Peggy Hall, is the expert. Most other advice stinks a bit.
Not really.

To the OP, Peggie asked me to ask him to EMAIL (NOT pm) her.

I've sent Mark a pm.
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Old 02-05-2015, 15:49   #10
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Re: Another holding tank vent question

What is a mushroom vent?

And who's this Miss Peggy?
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Old 02-05-2015, 20:04   #11
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Re: Another holding tank vent question

Make it easy on yourself.


C-Head portable composting toilets
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Old 02-05-2015, 20:55   #12
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Re: Another holding tank vent question

Quote:
Originally Posted by AlwaysFORSAIL View Post
The Head Mistress, Peggy Hall, is the expert. Most other advice stinks a bit.
I kinna like the pun!
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Old 04-05-2015, 08:38   #13
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Re: Another holding tank vent question

Thanks for all the input . For those who are against bladders overall, i sort of had no choice to go with a solid tank because of the limited space on the small boat. and now i definitely don't have a choice to return it as the bladder has had the inlet and outlets cut into it and installed. we use the boat for weekend daysailing and a few overnights and have free pump outs at the marina we are in so it should all work out well for the 6 months of sailing we get up here in Quebec.

So i guess my biggest take away from this is i got the wrong vent. I'll be sure to get a mushroom head with no screens instead.

Also will install the vent on the side of the hull in the shortest line possible just below the rub rail. I plan on suspending the vent attachment at the bladder so that it is not always collapsed and will have some headspace to hopefully improve air circulation.
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Old 04-05-2015, 08:42   #14
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Re: Another holding tank vent question

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Originally Posted by MarkVatcher View Post
I plan on suspending the vent attachment at the bladder so that it is not always collapsed and will have some headspace to hopefully improve air circulation.
I would confer with Vetus first. That may put a stress on the vent fitting that it is not built for. I would ask. This is not their first rodeo and I'm sure they understand the issues specific to bladders better than we do.
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Old 04-05-2015, 08:57   #15
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Re: Another holding tank vent question

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Originally Posted by thinwater View Post
I would confer with Vetus first. That may put a stress on the vent fitting that it is not built for. I would ask. This is not their first rodeo and I'm sure they understand the issues specific to bladders better than we do.
Good point, i'll see what they say. i was going by general consensus of what i have read on the internet about getting the best 'performance' out of the bladder.
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