New Holding Tank - odor from vent

After installing a brand new tank, hoses, vacuflush tank and sweet tank bubbler with a dose of Raritan KO in the tank - I'm noticing an odor from the vent line. I read Peggy's book cover to cover multiple times and don't understand why I'm getting an odor from the vent. I thought it was a dead crab at the marina at first then realized that dead crab was following me around. Sniffed the vent and there it was...

I have no fittings below the water line. All uniseal on top of the tank. Sweet tank bubbler running 24/7. Inside the boat has no smell at all. I looked in the tank and my sweet tank bubbler is working fine and bubbling the waste.

I'm debating on installing a charcoal filter in the vent which I wanted to avoid doing to promote the most oxygen flow in the tank. Should I give up and install the filter or is there something I may be missing? Could I have a bad bottle of KO and the bacteria isn't working? There is absolutely nothing in the brand new clean tank except water,waste, marine toilet paper and Raritan KO.

Appreciate any feedback.

For reference, here is my previous post when designing/installing my new wast system: http://www.trawlerforum.com/forums/s31/venting-holding-tank-sweettank-21348.html

We had a 46' trawler that had extremely bad odors from the holding tank. Talked to Peggy and per her advice put in the Groco Sweet Tank. After 2 hours running, the smell was completely gone. We never added any chemicals ever again. Kept that boat for 7 more years and had no smell at all. Don't know why you are still getting a smell. Try pumping it out and maybe not adding any chemicals and see what happens. Remember it takes some time for the air injection to take effect.

How long are you going between pump outs? Mine gets pumped out at least weekly when in use.

How new is this setup. It takes some time (my guess: a few weeks to a month) for the beneficial bacteria to adequately establish themselves.

No chemicals

I have no chemicals - only Raritan KO which is the Peggy approved natural bacteria additive. The tank has been pumped out one time since newly installed and is currently about a week since the last pump out and 50% full tank.

Maybe the bacteria hasn't had a chance to develop yet? I read in one of Peggy's posts that weekly pump outs should not be required in a healthy tank even in the hottest of summer months.

I'm away from the boat for a few days and am hoping when I get back the odor will be gone.

Any downside to adding a charcoal filter to the 5/8" vent? Since I have sweet tank running oxygen into the tank I'd imagine the downside of restricting the vent for airflow would not be an issue?

Anyone have perspective on adding a charcoal filter to my vent with a sweet tank system in place?

denisl said:

Anyone have perspective on adding a charcoal filter to my vent with a sweet tank system in place?

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I wouldn't. It would hinder your ability to back flush the vent when you pump the tank.

How long since you installed the bubbler and when was the tank last emptied?

In my mind you will not be able to get the vent completely odor free but it should get to the point where it isn't offensive.

After we installed the Sweet Tank, I could and did get within 4" of the vent and could not smell anything.

Is back flushing the vent sending water down the vent into the tank? Is that something I should do periodically? If so I'll need to change my vent through hull since it has a opening facing down.

The bubbler has been running since the new tank was installed and the tank was last emptied on July 3rd (also the first time the tank was every emptied since it is new this season).

When driving the boat, I get a periodic odor from the vent along side me. When at anchor/dock and on the swim platform I can smell if the wind is coming my way.

I suppose it could be comming from residue on the sides of the tank. Also, you should make sure to add some water to the tank after pumping out. If no water in the tank, nothing for be bubbler to interact with. We don't have a bubbler and used to use KO. We switched to Noflex last year with very good results. We add a tablespoon after pumping out, then another the following weekend when we get to the boat. No odors and we only have a single vent with no bubbler, so our tank is not aerated very well.

denisl said:

Is back flushing the vent sending water down the vent into the tank? Is that something I should do periodically? If so I'll need to change my vent through hull since it has a opening facing down.

The bubbler has been running since the new tank was installed and the tank was last emptied on July 3rd (also the first time the tank was every emptied since it is new this season).

When driving the boat, I get a periodic odor from the vent along side me. When at anchor/dock and on the swim platform I can smell if the wind is coming my way.

Click to expand...

I back flush the vent every time I empty the tank. You can do it even the cowled vents. While the holding tank is being sucked out, direct a stream of water from a hose up into the vent. The water will be sucked down the vent tube into the tank. It sometimes takes some contortion to do it but it works.

Silly question, but you did add more KO after the tank was emptied on the 3rd?

Another silly question, but be sure that any cleaners you use in the head won't kill off the bacteria. Maybe someone was too enthusiastic and used some bleach to clean the head? I use Raritan CP to clean the head.

Appreciate the responses. I only put KO in the tank and CP to clean the toilet. Good tip on getting the vent rinsed out - I'll definitely add that to the pump out procedure. When the tank was emptied on the 3rd I added more KO into about 2 gallons of water into the tank. My tank pump out is a top mount and leaves about 1" of waste in the tank.

I did not add any additional water to the tank after the pump out intentionally other than about 2 gallons flushed down the toilet with KO and maybe 1/2 gallon from the hose back flushing the pump out port to rinse it down.

The tank now is about 50% full with a good amount of KO in there (I put an extra 4oz or so when I locked up the boat on Sunday). Sweet tank bubbling away as well. Hopefully when I get back to the boat on Saturday my aerobic bacteria will be in full force and the odor will go away. If not, I may try Noflex and if that still doesn't work then resort to adding back in a charcoal filter.

If the odor was very random I wouldn't mind. I replaced all my waste system components last season because my wife said the smell down below was becoming noticeable. If I just moved the smell to the cockpit she will not have much confidence in my repairs! Plus it's not to pleasant for guests.

Sounds like you have done everything the way you should so I have no idea. Hopefully Peggy will chime in as she can usually get to the heart of the problem.

When we bought our boat about 9 years ago we had a terrible odor from the tank and vent. It had a charcoal filter and I removed it. the smell went away within a week. I wouldn't use it.
John