Holding tank vent

mregan · November 18, 2012, 07:03:39 AM

I have a leaking holding tank vent stanchion on my "new" '86. I've been reading some of the old holding tank threads. There was mention in one thread to remove the vent stanchion, glass over the hole and install a thru hull below the toe rail and vent from there. Peggy Hall had commented on one thread to install a clam shell cover over the thru hull with the opening pointed aft. When the rail is buried, the clamshell would prevent water from getting into the tank. Has anyone tried this method? Didn't see any followup in the threads where someone has actually tried it.

Second item: Has anyone installed a "bubbler" in the holding tank to aerate the tank constantly. I've read Peggie's book about providing properly venting for the tank to eliminate odors. The proper routed vent will aerate the tank itself but it seems the way our vents are routed, it won't provide proper ventilation. I was thinking about drilling a 1/4" hole into the vent elbow off the top of the tank. Dropping in a 1/4" tube into bottom of the tank and hooking the other end up to a fish tank type bubbler. I figured the constant bubbling would provide the aeration the tank needs. Was going to install a 120v bubbler. I'm at a slip all week long on shore power so the bubbler would work all week and only be off on weekends. Thoughts?

Stu Jackson · November 18, 2012, 10:01:48 AM

This is the discussion of the vent with pictures, the title his water tank vent but the pictures show the holding tank vent. http://c34.org/bbs/index.php/topic,6293.0.html

Peggie discusses the clamshell, but the skipper who installed it says it isn't needed.

If you vent it properly, you don't need a bubbler. The bubbler isn't a good idea, since the issue is the anerobic one, the need to provide oxygen to avoid the smell. The other concept was moving air, not bubbling the contents.

We use Odorlos, and it works just fine, even with the old vent still attached.

Dave Spencer · November 18, 2012, 12:16:12 PM

mregan,
I added a holding tank vent just below the toerail earlier this year and documented my method in this thread (starting at reply #17).
http://c34.org/bbs/index.php/topic,6861.15.html
I now have two vents. After using it for a great summer of sailing, I noted that in very light wind on a port tack, I would occasionally get a foul smell wafting out of the stantion vent as air flowed into my forward vent, picked up the smell in the tank and vented out the original stantion vent. This was easily fixed with about 5cm of trusty white vinyl tape to plug the aft vent hole when sailing in light air on a port tack. The jury is still out for me as to whether two vents are better than one. Certainly the OEM vent is inadequate and the forward vent is better but two vents may not be ideal the way I have it set up. However, I figure it is far easier to plug the aft vent with a short length of tape when necessary than go through the pain of eliminating the stantion vent.
I see no need for a clamshell to protect the forward vent from water when heeled over.
I wouldn't consider a bubbler.
Feel free to contact me if you need any further thoughts or want to discuss adding a vent just below the toerail. I'd be glad to offer any help you need based on my recent experience.

mregan · November 18, 2012, 02:00:19 PM

Should have been calling the bubbler an aerator/air pump. By adding one, I would be introducing oxygen into the tank which I think is what is needed to break down or stop the formation of the odor causing bacteria. (I have Peggie's book at the boat so I'm going by memory) I had seen a system by Groco called the Sweet Tank. http://www.groco.net/00-sanitation/stk-install.htm. Was thinking the fish tank air pump would do the same thing for a lot less cost.

Stu Jackson · November 19, 2012, 10:12:51 AM

Before you go to all that trouble, have you connected your head inlet to the sink drain yet?

Head Odors 101.1 - "T" into sink drain: http://c34.org/bbs/index.php/topic,5755.msg38216.html#msg38216

Exodus · November 19, 2012, 03:03:33 PM

I replaced my tank vent with a through hull just below the toe rail and a little bit aft of the former vented stanchion. I also glassed in the hole for the vented stanchion and replaced it with a regular stanchion. I did not add the clam shell over the through hull because I could not find one locally at the time I did the project and never added it. The clam shell is really not needed in my opinion. I am really happy with the new vent set up and have had it for over a year now.

Also I would not add the bubbler you are talking about. Seems to me if you are stirring up Sh*t it is going to stink worse. I may be wrong on that, but just my .02! I think a combination of good tank vent, chemicals and frequent pumpouts should do the trick.

Fred Koehlmann · November 19, 2012, 05:35:36 PM

We also replaced the existing stanchion vent when we installed a new holding tank this spring. Glassed in the through deck hole and ground off the extension on the stanchion and rebedded it in place. Now the space behind the electrical is DRY.

The new vent line goes foward and out through the hull from behind the port hanging locker in the V-berth. That point of the hull is typically not under water and I didn`t bother with a clam shell either.

We do pump out frequently, but even on our vacation it was over a week before some odour was noticed, and only when the wind was just right. Maybe a second vent to the transom would have helped by-pass the cockpit !

KWKloeber · October 21, 2016, 12:20:42 PM

I'm interested to hear if anyone has installed an aerator system that *worked* and is happy with the results? (or otherwise.)
Basically an update on the one reply I see that the Groco system is a waste of several hundred boat bucks.

Thanks
Ken

Roland Gendreau · October 22, 2016, 07:29:35 PM

I installed a 12 volt aquarium air pump to enhance the holding tank vent, which in our case is the standard stanchion vent We let it run when the boat was sitting on the mooring and shut it off when aboard, as it did make a noticeable hum that was distracting. The air pump seemed to lessen the tank odors noticeably. I drilled a hole in the top of the tank, and threaded the hole to accept a threaded adapter with the hose from the air pump on the other end of the adapter. So the air being pumped in doesn't bubble through the contents, it just brings more air into contact with the surface of the tank contents, just as a better vent system would be expected to do. I did this more as an experiment to see if better venting would help; I do plan to install a new vent below the rub rail as others have done.

KWKloeber · October 22, 2016, 08:29:51 PM

Quote from: Roland Gendreau on October 22, 2016, 07:29:35 PM
I installed a 12 volt aquarium air pump to enhance the holding tank vent, which in our case is the standard stanchion vent We let it run when the boat was sitting on the mooring and shut it off when aboard, as it did make a noticeable hum that was distracting.

Roland, I wonder if in your case (surface air only,) a small pancake fan necked down to the tubing size (say mounting the fan on a funnel) might deliver more O2 and be quieter?

-ken

Indian Falls · October 23, 2016, 07:53:33 AM

I have yet to find on any sailboat forum an instance where " we did this... and now there is no odor".
It seems people have gone to a great deal of trouble only to have the results being "I think its better".
My conclusion from all the reading I've done is there is nothing on the C34 you can do to eliminate tank odor.
Rather than work my butt off trying to install a side thru hull or add running machinery or dual vents, I just go with adding odor control fluids to the tank, pumping out often, and using only the "potty tack" (starboard) for bathroom breaks when sailing. Two vents without some way of forcing air through is nothing more than a bigger single vent. I'll bet money a tank with no top, full of whats in our tanks still stinks! Ever leave a toilette un-flushed for a long weekend away from home?

Roland Gendreau · October 24, 2016, 05:55:25 PM

Quote from: KWKloeber on October 22, 2016, 08:29:51 PM
Quote from: Roland Gendreau on October 22, 2016, 07:29:35 PM
I installed a 12 volt aquarium air pump to enhance the holding tank vent, which in our case is the standard stanchion vent We let it run when the boat was sitting on the mooring and shut it off when aboard, as it did make a noticeable hum that was distracting.

Roland, I wonder if in your case (surface air only,) a small pancake fan necked down to the tubing size (say mounting the fan on a funnel) might deliver more O2 and be quieter?

-ken

Ken, that is an interesting idea but I wonder if the funnel and smaller tubing might have enough pressure drop to reduce the flow from the pancake fan significantly. Also, I did not pay much for the aquarium air pump so maybe a more expensive model might be quieter.

KWKloeber · October 24, 2016, 07:03:45 PM

Quote from: Roland Gendreau on October 24, 2016, 05:55:25 PM
Quote from: KWKloeber on October 22, 2016, 08:29:51 PM
Quote from: Roland Gendreau on October 22, 2016, 07:29:35 PM
I installed a 12 volt aquarium air pump to enhance the holding tank vent, which in our case is the standard stanchion vent We let it run when the boat was sitting on the mooring and shut it off when aboard, as it did make a noticeable hum that was distracting.

Roland, I wonder if in your case (surface air only,) a small pancake fan necked down to the tubing size (say mounting the fan on a funnel) might deliver more O2 and be quieter?

-ken

Ken, that is an interesting idea but I wonder if the funnel and smaller tubing might have enough pressure drop to reduce the flow from the pancake fan significantly. Also, I did not pay much for the aquarium air pump so maybe a more expensive model might be quieter.

Yeah, and I suppose a check valve in the line would be necessary (block odors backing up the line if the fan was off?) Might not be practical, but possibly worth some testing.

Or, put your pump inside some soundproofing (foam-lined box, one end open?)

-ken

Stu Jackson · October 25, 2016, 07:20:07 AM

Quote from: Indian Falls on October 23, 2016, 07:53:33 AM
I have yet to find on any sailboat forum an instance where " we did this... and now there is no odor".
It seems people have gone to a great deal of trouble only to have the results being "I think its better".
My conclusion from all the reading I've done is there is nothing on the C34 you can do to eliminate tank odor.
...........

There is great merit in those observations. I have experienced the same, albeit without enlarging or modifying our vent, while some (though few) have been successful with improved vents. Even using Odorlos, after a long layup there is a whiff the first few pumps. On our trip north there was no odor. Frequent daily use had precluded it, reflecting my earlier cruising experiences. Solution? Use your boat more often!

Roc · October 26, 2016, 03:55:23 AM

I remember reading one of Peggie's posts that putting an aerator doesn't do anything. What is key is a good vent, that is run correctly (not straight up from the tank, but a gradual slope horizontally). Also the vent needs to be large (1" or so in diameter). If getting an odor on the first few pumps, wouldn't that be stagnant seawater from the insides of the bowl that come out? If so, flushing with fresh water would solve that. (I flush with fresh water and never have that issue). I put a dose of Odorloss when shutting down for the weekend.