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Old 29-04-2010, 16:30   #1
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Holding Tank Vents and Microbes...

Hi all! Does anyone on the forum have experience with venting their blackwater tank with multiple / large vents to promote aerobic bacterial growth? I know that the awful smell of most holding tanks is caused by anaerobic bacterial growth, and that Peggy Hall recommends large vents, but the Sealand tank I am looking at only comes with a 5/8" vent fitting. I was thinking about adding another line, and then mounting one vent fitting on the hull with a clamshell facing forward (to act as a ram air scoop) and another with a clam facing aft (to pull a vacuum) in order to promote airflow in the tank. Any thoughts from people who have went this route instead of the chemical / vent filter route? Thanks, Chris
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Old 29-04-2010, 16:56   #2
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If you mount a rear facing one in the cockpit, that should give you a lot of outflow...
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Old 29-04-2010, 17:34   #3
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We custom ordered a tank with a 1" vent on it, and use a 1" vent line that is about 24" to a 1" fitting that goes outside of the hull, just under our caprail. We then put a clamshell cover from seadog over it, facing about 10 degrees down and aft. We have a Lavac head and use only fresh water (we have over 220 gallons of freshwater tankage on board) and between the fresh water, odor proof hoses and the seal on the lavac head (THey are manual pump, but uses a vacuum to flush) we do not have an odor problem. We also use about a tablespoon of active yeast in our holding tank which is 40 gallons, and no problems with odor. INcidently as fate would have it, our tank is 6" from our 24,000 BTU AC intake vent in the main salon and if it were to stink it would take about 10 seconds to know it. We ditched our sealand filter and have never had a bad odor out the vent yet....A few weeks back we had guest onboard, and they couldn't belive there was not odor from the head....Apparently they had a few odors in their boat they were wrestling with...
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Old 29-04-2010, 18:28   #4
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Thank you yacht_planB! Not so much, SenorMechanico... My new Lavac arrived today! First thing we thought when we pulled it out of the box (it's the "Popular" model) is "OH MY GAWD! How do you fit on that thing?". It looks like a toy! We are using the thru the bulkhead manual pump mount, and I think its gonna be a nice looking installation when it's done. As for the vents, I dont know if I can get anything larger than 5/8" with the stock Sealand...but I might be able to add another one. I would consider another tank, but I really like the quality of the Sealand, and they have some sweet features: A valve that keeps the tank from collapsing if a huge pump out machine is used and the vent is clogged, great wall thickness, and TWO outputs; one for the deck pumpout, and one for the on-board pump. Glad to hear you are odor free, and thanks for the yeast tip! Chris
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Old 29-04-2010, 18:47   #5
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I have one of the Sealand holding tanks - happy except for the charcoal filter. Even though my vent line had a pretty good size loop, some water got past this down into the filter during a rough passage (wasn't tank overfill). Next thing I knew, I had no vent (and boy do you find this out quick!).

I took off the vent and cut it in half with a hacksaw (it's just 2" PVC pipe under a fancy label). Inside the wet charcoal had expanded into a solid black mass the consistency of damp beach sand - it completely filled the pipe.

I know several people who claim happiness with the Groco Sweet tank. It's a bubbler that pumps air into the tank 24 hours a day (about 3 watts power). It's a bit pricey ($200) but means an end to chemicals and the smell - supposedly. It also means a small vent line is just fine.

Anyone on the board have any experience with the Sweet tank?

Carl
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Old 29-04-2010, 18:56   #6
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Anyone on the board have any experience with the Sweet tank?
We should hold a design competition here on the forum to design a pump that aerates the holding tank using only the motion of the boat. Might be a problem in marinas though...
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Old 29-04-2010, 19:12   #7
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We've had good luck so far after adding a second 3/4" vent hose to our holding tank and using KO tank treatment. I wonder if using yeast instead of KO would do nearly the same job? Why not? It would also cost a lot less the nearly $20/pint of KO. The bye product of yeast fermentation is alcohol after all.
I do believe that having enough air and using a bacteria/microbial treatment is the way to go for holding tanks. Peggy Hall's book(let) was quite useful.
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Old 29-04-2010, 19:19   #8
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Jury is still out, but last winter I added a second vent line for each holding tank so there would be a vent on each side of each hull. With only one vent, wind pressure would force fumes up through the head...ugh. But so far it seems to have solved that problem. Should help the bacteria breathe as well.

Outboard vent line is 3/4, inboard is 5/8.
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Old 29-04-2010, 19:35   #9
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I have used 2'' pvc screw couplings to be able refill with new charcoal from the fish store Saves a bunch of money as a new filter is $80
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Old 29-04-2010, 20:06   #10
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Jury is still out, but last winter I added a second vent line for each holding tank so there would be a vent on each side of each hull.
What type of fitting did you use to add a line to the tank? Something with threads and a gasket I presume?
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Old 29-04-2010, 20:19   #11
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" if using yeast instead of KO would do nearly the same job? Why not? It would also cost a lot less the nearly $20/pint of KO. The bye product of yeast fermentation is alcohol after all. "

CalebD - That would make some cra$#y alcohol. LOL <G> Seriously I used to live in an RV when I was much younger and the active yeast kept the odor from occuring and no other chemicals needed... Fresh water makes a huge difference as no sea critters are dying in the tank either...
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Old 30-04-2010, 10:07   #12
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Met a guy in Subic who was building a couple big trawlwers...he was using a very small aquarium pump to aerate his tanks...doesnt sound like it takes a lot of air.
Good idea on the air pump design competition Chris...I wonder just how much air we are talking about?
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Old 30-04-2010, 10:58   #13
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Peggy rocks. She's been online in various forums well before there was a public internet, and she's yet to be proven wrong on any point she's made. Her one failing might be that...shhhh! She prefers power boats. :-)
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Old 30-04-2010, 17:10   #14
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CalebD - That would make some cra$#y alcohol. LOL
We used to have this sparkling wine stuff made near us called "Champale" which was quite possibly made this way...that is, in the holding tanks of cruising boats... Just kidding, in case it's still made somewhere!

James, if we had a competition, I can almost guarantee you'd win it! If we did design a bubbler, it wouldn't have to run continuously... just a few seconds every half hour or so... What do you think? Most likely solar with a low draw timer set-up..
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Old 30-04-2010, 17:23   #15
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I remember Champale which was neither Champagne or Ale.

I used to dabble a bit in making wine and various fermented beverages in my youth. The only real problem I can see with using active yeast as a treatment for the holding tank comes from my experience of trying to make Mead (honey wine). The glass gallon jug I used for that sort of blew its top one night (exploded, after a fashion). There must have been a lot of yeast and too much sugar in the mixture so it foamed up and blew it's top. In the holding tank I guess this could be bad news for the air vents if this happened. Kind of gives a new insight into the term 'honey wagon'.
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