I've tried various tank treatments (most recently Odorlos) and I've come to the conclusion that a black water tank is going to have a smell as long as you're standing next to the vent stack on top of the boat. That's fine for RV folks that don't spend much time on their roof, but my roof is the best place to spend a summer night under the stars.

Having decided that tank treatments control rather than eliminate smell, I am giving thought to extending my vent stack. I have a 1.5" stack that terminates in a cap just above my roof. If I add a 90 degree bend and travel horizontally about 6 feet, I can make another 90 degree bend to go straight up and attach a 10 foot vertical extension to the leg of a permanent canopy. That would raise the top of the stack ten feet over the roof surface and four or five feet above my guests' and my noses. I realize the horizontal portion of the stack would need a slope; I have room to give it a standard .25" per foot slope. I could add a cap, but Lake Powell averages about 7 inches of rain in a year. I don't think that will add much water to my tank.

I have to imagine I'm not the only one who has experienced a smell from black water. It seems that many enjoy time on their roof. So I'm thinking that someone has to have tried something like this. Or at least considered it and decided it was a stupid idea. I'd love anyone's thoughts on whether this is a great idea or whether I should scrap it.

Edited: 08/10/2010 at 10:35:06 AM by endurance

Common practice on many boats is to vent the tank out the side of the boat under the deck.

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OLD HOUSEBOATER

Venting your tank through the roof is actually causing your odor problems, because a long vertical vent pipe makes it impossible to keep the environment inside the tank aerobic--which is essential in preventing odor.

Rerouting your vent to go out the side of the hull is one solution...but a holding tank aeration system would be the best solution for you because of your climate. The warmer bacteria are, the more active they are...making it very difficult to keep them functioning aerobically.

Check out the Groco Sweetank system

http://www.groco.net/SVC-MAN-07/Sec1/pdfs/STK.pdf

When installed, operated and maintained according to directions it completely eliminates holding tank odor without the need for any tank product.

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Peggie Hall, Moderator
Specializing in marine sanitation since 1987, Author: "Get Rid of Boat Odors--A Guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor."
[L=http://shop.sailboatowners.com/books/detail-books.htm?sku=66438&cat=1304[/L]

Hmmm wouldn't TWO vents work even better, say one on each side of the boat???

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

This looks very interesting, I am not sure how easy it would be to retrofit into my existing tank. I would be interested to hear from someone that has installed it.

We battle the smell every weekend. We have a large vent (1 1/4) but the smell is always present.

Fred

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Yesterday was the best day of my life..... I bought a Houseboat!! Check out our blog of our houseboat refurbish!! http://fredsfriendlyblogspot.blogspot.com/

As usual, you all have given me great insight. I think I'll take all of your thoughts and add it to what I learned from one boat builder's website and take this a step at a time:

First, I'll go ahead and extend my vent. My heads are direct-drop, so my tank gulps a fair amount of oxygen with each flush. I don't smell anything with flushing; the only problem is with the vent on top. So if I move the problem up to where the lighter-than-air smelly gasses escape upward, I won't care if I have a little anaerobic activity in my tank. I was going to use white PVC, but now I'm thinking that black ABS might aid in heating air and causing a draw much like a fireplace flue. This may be as far as I have to go.

Second, if I have any remaining odor, I think I'll add a 1.5" threaded fitting to the top of my tank at the opposite end from my existing vent. I have room to reach in, drill a hole, and solvent weld a fitting in place. I also have room to add another vent that rises above the tank. I could even add an air admittance valve like this one. Either way, the tank should then take in lots of air to replace that which rises out my newly-extended vent stack. If it works, it will be much like a Groco Sweetank system, but it will be solar powered. I can brag about this to my green-minded friends.

Third, if I still have odors, I can take the action Peggy recommended. It turns out that 1.5" is the exact size a Groco Sweetank needs to screw into the top of my tank. So the Groco bubbler would just go in place of my 1.5" second vent. That would be the gold standard, but I'm betting I won't need to go that far.

I hope to report back with good results. If anyone has any criticism of this plan, please let me know before I do anything I'll regret.

You could put a flag on top of that pipe to disguise it.

Here is the report I promised. I extended the vent stack about 10 feet above the roof. Odor problem solved. There are no odors at any time of day or night in the boat, on the top deck, or anywhere. Unless you count being in a bathroom when someone is "using" the toilet But that's more of a human issue than a boat issue.

I've been dreaming of an odor-free boat for some time. If only I would have known the fix was so easy.

Many thanks for your insights. They worked!

Can you post a picture please. You must not have any bridges to clear.

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OLD HOUSEBOATER

Could always install a screw or slip fitting at roof level, so in that situation the extension could be removed.

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Willie
She's a tired old barge but she's paid for! http://s71.photobucket.com/alb...p;current=ef324993.pbw

Peggie,
I read the info about the Sweet Tank pump.  I curious about having 2 tanks and if there is a need for 2 pumps.  My tanks are joined by a 3 and 1/2 pipe.  Just wondering.  Thanks.

You'd need two piping systems...and I suspect two pumps as well. But it would be worth asking Groco if one pump is powerful enough to aerate both tanks, and if so how to connect the piping from both tanks to it. Give 'em a call at 410-712-4242.


-------------------------
Peggie Hall, Moderator
Specializing in marine sanitation since 1987, Author: "Get Rid of Boat Odors--A Guide to Marine Sanitation Systems and Other Sources of Aggravation and Odor."
[L=http://shop.sailboatowners.com/books/detail-books.htm?sku=66438&cat=1304[/L]