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Old 07-31-2021, 11:31 AM   #1
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Holding Tank Vent Filter

Searching for an in-line filter on my holding tank vent. The two holding tanks are on either side of the aft-cabin bed. The only access that Iíve found to the tanks matches up with the inspection port. So, I canít see any of the hose connections let alone an in-line filter. I did find the hose connection to the thru-hull. It was behind the aft port corner trim piece behind a speaker.

Is it possible that there never was a filter on the vent lines?
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Old 07-31-2021, 11:40 AM   #2
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Searching for an in-line filter on my holding tank vent. The two holding tanks are on either side of the aft-cabin bed. The only access that Iíve found to the tanks matches up with the inspection port. So, I canít see any of the hose connections let alone an in-line filter. I did find the hose connection to the thru-hull. It was behind the aft port corner trim piece behind a speaker.



Is it possible that there never was a filter on the vent lines?
Not sure about your boat, but it would be very likely that it doesnít have a vent filter. In general, I think they are a bad idea.
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Old 07-31-2021, 12:09 PM   #3
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So, you prefer a chemical treatment instead?

What are the cons to vent filters?
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Old 07-31-2021, 12:33 PM   #4
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So, you prefer a chemical treatment instead?

What are the cons to vent filters?

The best way avoid holding tank odors is to provide lots of oxygen to the tank to encourage the growth of aerobic bacteria as opposed to the anaerobic bacteria which smells bad. Vent filters reduce the air flow through into the tank. They also can get clogged which can make it harder to pump out the tank.

As for tank treatment, I have used Raritan K.O., No-Flex, or simple sodium percarbonate. The KO, as I understand it, introduces health aerobic bacteria to the tank so if you have enough air exchange it works really well. No-Flex and sodium percarbonate introduce oxygen to the holding tank as is breaks down.

I eventually made and installed a tank aerator to provide good air exchange in the tank. That is by far the best solution.

There are others much smarter than I on this. You may try doing a search for threads on holding tank vents and you will get lots of information.

https://www.amazon.com/New-Get-Rid-B...7752699&sr=8-1

That is the best resource available for holding tank issues.
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Old 07-31-2021, 12:35 PM   #5
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Hi Ray - I highly recommend you read Peggie Hall's book 'Get rid of boat odors'. Peggie is the Guru of boating sanitation and a wonderful person. She addresses the cons of holding tank vent filters well in her book. She is also frequently online her on TF - HeadMistress is her username.
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Old 07-31-2021, 12:48 PM   #6
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Vent filters restrict aerobic bacteria that is essential in holding tanks. The more air coming in the better the bacteria grows.Filters are suppose to cause less odor exiting your tank,so they say. Ditch the filter and allow the air to flow.
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Old 07-31-2021, 01:03 PM   #7
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Hi Ray - I highly recommend you read Peggie Hall's book 'Get rid of boat odors'. Peggie is the Guru of boating sanitation and a wonderful person. She addresses the cons of holding tank vent filters well in her book. She is also frequently online her on TF - HeadMistress is her username.
I also recommend Peggies book,great practical knowledge.
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Old 07-31-2021, 02:37 PM   #8
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A little bio-physics 101: When organic matter breaks down AEROBICALLY (oxygenated) it converts to CO2 which is odorless. When it breaks down ANAEROBICALLY it generates hydrogen sulfide and sulfur dioxide which not only stink but are also toxic, and methane which is odorless but flammable. Vent line filters actually help to create the very problem they're sold to so solve because they impede the exchange of oxygen with gasses in the tank that's essential to PREVENTING odor by simply blocking odor. The tank product used matters, but improving the ventilation to the tank is the key eliminating holding tank odor--odor out the vent---because oxygen prevents it from occurring in the first place.


Thanks for all the "plugs" for my book! Its title (my publisher's idea) is a bit misleading...'cuz although it does deal with every source of odor on a boat and how to cure, or better yet PREVENT 'em, it's actually a comprehensive "marine toilets and sanitation systems 101" manual that explains the laws, describes all the types of systems and how they work, and will help you learn how to operate and maintain your system to prevent 99% of problems instead of having to cure 'em. 'Cuz you get to do any preventive maintenance on your terms when it's convenient...the need to cure a problem never happens when it is! And I'm always glad to answer any questions it doesn't.

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Old 07-31-2021, 02:53 PM   #9
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IMO vent filter ENSURE that your tank will be anaerobic (the smelly kind) and your tank will smell bad. Then you NEED the filter to prevent the escape.
A better approach is to ensure aerobic (not smelly) bacteria predominate and there is no need / use for a filter.
Large, short, straight vent line & straight thru mushroom fitting alow the most air flow.
NoFlex or generic sodium percarbonate (a little each day) has workedwell for me.
I built & installed a DIY bubbling system for about $40 and it has worked perfectly.
See Bacchus Website... Project.... DIY Holding Tank System for details.
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Old 07-31-2021, 03:40 PM   #10
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All righty then. I just flushed a couple of Tbls of Noflex in each head. Will do so again tomorrow to make sure it made it makes it past the vacuflush tank. Will see if my dock neighbors are happy.

WE get pumped out every Wednesday and we use only fresh water. I’m thinking the Noflex should keep my neighbors happy.
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Old 07-31-2021, 07:05 PM   #11
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3-4 months ago I installed a 12v air pump (think fish tank) to avoid odors when pumping at sea. Super oxygenating the waters promotes good bacteria ergo no odors. After a few days there was a slight smell on the vent area of the tank. That has now disappeared. So it looks like some success has been achieved. I have a 100gall holding tank. My previous boat was always a tad odorous when offshore pumping at sea. The whole thing only took a few hours to fabricate.
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Old 07-31-2021, 08:10 PM   #12
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All righty then. I just flushed a couple of Tbls of Noflex in each head. Will do so again tomorrow to make sure it made it makes it past the vacuflush tank. Will see if my dock neighbors are happy

Unlikely if flushing No-Flex is the only thing you've done.



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Old 07-31-2021, 08:37 PM   #13
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Yes, if you have a vent filter get rid of it and maybe add a second vent. That will help get oxygen into the tank.
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Old 07-31-2021, 10:14 PM   #14
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The best way avoid holding tank odors is to provide lots of oxygen to the tank to encourage the growth of aerobic bacteria as opposed to the anaerobic bacteria which smells bad. Vent filters reduce the air flow through into the tank. They also can get clogged which can make it harder to pump out the tank.

As for tank treatment, I have used Raritan K.O., No-Flex, or simple sodium percarbonate. The KO, as I understand it, introduces health aerobic bacteria to the tank so if you have enough air exchange it works really well. No-Flex and sodium percarbonate introduce oxygen to the holding tank as is breaks down.

I eventually made and installed a tank aerator to provide good air exchange in the tank. That is by far the best solution.
Dave, with the aerator are you still using a chemical treatment? Not using the chem would be the only reason for me. Peggy has said vent on either side and 2 inch lines IIRC. Again, can chemicals be eliminated with aeration methods.
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Old 08-01-2021, 12:11 AM   #15
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We put a Groco Sweetank system in a previous boat on Peggies advice. We never put any chemicals in after that for the 8 more years we owned the boat.
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Old 08-01-2021, 06:31 AM   #16
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Originally Posted by HeadMistress View Post
A little bio-physics 101: When organic matter breaks down AEROBICALLY (oxygenated) it converts to CO2 which is odorless. When it breaks down ANAEROBICALLY it generates hydrogen sulfide and sulfur dioxide which not only stink but are also toxic, and methane which is odorless but flammable. Vent line filters actually help to create the very problem they're sold to so solve because they impede the exchange of oxygen with gasses in the tank that's essential to PREVENTING odor by simply blocking odor. The tank product used matters, but improving the ventilation to the tank is the key eliminating holding tank odor--odor out the vent---because oxygen prevents it from occurring in the first place.


Thanks for all the "plugs" for my book! Its title (my publisher's idea) is a bit misleading...'cuz although it does deal with every source of odor on a boat and how to cure, or better yet PREVENT 'em, it's actually a comprehensive "marine toilets and sanitation systems 101" manual that explains the laws, describes all the types of systems and how they work, and will help you learn how to operate and maintain your system to prevent 99% of problems instead of having to cure 'em. 'Cuz you get to do any preventive maintenance on your terms when it's convenient...the need to cure a problem never happens when it is! And I'm always glad to answer any questions it doesn't.

--Peggie
Hi Peggie. I've been using this stuff, Is this good or bad?


https://www.amazon.com/dp/B077VWX6BB...roduct_details
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Old 08-01-2021, 10:11 AM   #17
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Peggy has said vent on either side and 2 inch lines IIRC. Again, can chemicals be eliminated with aeration methods...

You recall incorrectly. I'm misquoted on this more than anything else.

I have said that 2 vent lines MAY be advisable in installations that make it impossible for 1 vent line to provide necessary ventilation, but I've never recommended a 2" vent line nor insisted that it has to exit on both sides of the boat. A single 1" vent line or at most a 1.5" in a short (up to 5') straight line that has no more than a 45 degree rise to an open bulkhead or "mushroom" thru-hull is enough to do the job one most boats. There are a few installations that won't allow anything but aeration to work.

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Old 08-01-2021, 10:37 AM   #18
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Hi Peggie. I've been using this stuff, Is this good or bad?

https://www.amazon.com/dp/B077VWX6BB...roduct_details
If you're happy with it, it's your boat. However, I'm automatically skeptical of any product that refers to a holding tank as a septic tank (anaerobic, the opposite of aerobic). More importantly, that it's a chemical product that the mfr touts only as "non-formaldehyde" is a big red flag for me 'cuz formaldehyde is just one of the toxic chemicals used in tank products...quaternary ammonium compounds and gluteraldehyde are the other most commonly used highly toxic chemicals...all of which work by killing bacteria, which is not what you want to do.

And btw.."biodegradeable" is actually a meaningless feel-good term typically used to mislead people into confusing it with "environmentally friendly"...formaldehyde is actually biodegradable, it just takes a quite a while TO biodegrade, doing considerable environmental harm meanwhile. I'd need to see the SDS for this product to know what "non-formaldehyde" chemical is the active ingredient and what else is in it that could potentially harm the plumbing or may be unsafe to store around children or pets.

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Old 08-01-2021, 10:56 AM   #19
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Peggy has said vent on either side and 2 inch lines IIRC. Again, can chemicals be eliminated with aeration methods...

You recall incorrectly. I'm misquoted on this more than anything else.

I have said that 2 vent lines MAY be advisable in installations that make it impossible for 1 vent line to provide necessary ventilation, but I've never recommended a 2" vent line nor insisted that it has to exit on both sides of the boat. A single 1" vent line or at most a 1.5" in a short (up to 5') straight line that has no more than a 45 degree rise to an open bulkhead or "mushroom" thru-hull is enough to do the job one most boats. There are a few installations that won't allow anything but aeration to work.

--Peggie
Thanks for the correction.
Cross contamination is what it is. Following to the groco site shows a 'T' vent line, did not look for size. Steve D'Antoni has an article that suggest two lines up to 1-1/2. So the info goes in and gets mixed up.

If passive air from a 1" single line does the job in the air space above sewage, then why bother installing a bubbler like Groco and not as suggested just plumb to top a fish tank aerator of tank to keep moving fresh air?
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Old 08-01-2021, 11:08 AM   #20
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If you're happy with it, it's your boat. However, I'm automatically skeptical of any product that refers to a holding tank as a septic tank (anaerobic, the opposite of aerobic). More importantly, that it's a chemical product that the mfr touts only as "non-formaldehyde" is a big red flag for me 'cuz formaldehyde is just one of the toxic chemicals used in tank products...quaternary ammonium compounds and gluteraldehyde are the other most commonly used highly toxic chemicals...all of which work by killing bacteria, which is not what you want to do.

And btw.."biodegradeable" is actually a meaningless feel-good term typically used to mislead people into confusing it with "environmentally friendly"...formaldehyde is actually biodegradable, it just takes a quite a while TO biodegrade, doing considerable environmental harm meanwhile. I'd need to see the SDS for this product to know what "non-formaldehyde" chemical is the active ingredient and what else is in it that could potentially harm the plumbing or may be unsafe to store around children or pets.

--Peggie
I'm not particularly attached to this product other than its ease of use. I'd be very interested in what you think is the best additive to use. I had a new holding tank installed 2 years ago, so it should be in fairly good shape for whatever is advisable. I have a vent and no filter, but my wife sometimes complains of odor. Unfortunately (sometimes fortunately) I have lost my sense of smell in recent years so I rely on her feedback. And of course I trust whatever you think is best. Thanks for your help!
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