Holding Tank Vent Charcoal Filter

Benny17441 · Oct 10, 2018

Charcoal filters, what are you thinking, using black water to make coffee? Your system is designed to contain odors, check the head seals, plumbing, hoses and valves. attack the cause, not the symptoms.

Stu Jackson · Oct 10, 2018

jviss said:
The sanitation system works fine, and I'm not interested in flushing with fresh water, or T-ing into the head sink drain, etc. I am, however, very interested in the idea of being able to filter out, absorb those odors.

This could be translated to:

"I may know the solution to my problem, but I don't want to do it."

This is another one of those "how long have you been here on sbo and not been reading?" topics, jviss. I really thought your longevity would help with head issues. Pun intended.

Just kidding...

Peggie Hall has commented no filters on vent lines so many times, she's canned the reply into a cut & paste. Perhaps you don't read the recurring posts on this very topic.

Improve the vent line to make the contents aerobic, use Peggie-recommended materials like KO and the green stuff (Odorlos) and T into the head sink for use at ONLY the LAST flush of the day (unless your new boat has some oddball layout that precludes that, but you only said you didn't want to, not that you couldn't).

Most of us have learned by reading Peggie's book and her posts on this and other boating forums.

Filters on vent lines are not a good idea.

Ron20324 · Oct 10, 2018

jviss said:
Why is that, Stu? Why are filters on vent lines not a good idea?

I believe it was in another thread just yesterday Peggie pointed out the wet charcoals expands then acts like a plug in the vent line- it's purpose defeated by it's own characteristics. You'd be better off putting in a larger vent line to vent the tank .

thinwater · Oct 10, 2018

Yes, the formaldehyde in several products will kill bacteria, but formaldehyde is also biodegradeable, so once it is diluted through several good pump-out cycles the problem will go away.

Yes, minimizing the odor in the tank through bio-augmentation and ventilation is generally the best approach. Try that first. However, there are also boats where vent locations are problematic, and vent filters do work. I've done it both ways, in each case for over 5 years, and they both work if done properly. It can also be done incorrectly, which does not invalidate the process. But canister location is very important and it must stay dry. This will be difficult to accommodate on some boats. It was easy on my catamaran.

This link covers a DIY approach. There is also information in Practical Sailor and Good Old Boat magazines.
http://sail-delmarva.blogspot.com/2011/04/holding-tank-odors-vs-carbon-vent-filter.html

PVC pipe is the best choice. The foam is require BOTH to retain the carbon fines, and ALSO to prevent the carbon from moving. By providing positive compression, the carbon does not rattle around and turn into dust. A wire screen is not enough. This has been proven in automotive carbon canisters.

The carbon should last about 3-5 years if located so that it stays dry. It does self-regenerate with in-out breathing, to considerable extent, since sulfides in the gases react on the surface of the carbon to form sulphur (you can see the sulfur when you open a spent canister after 5 years). This chemistry is well know.

There is also no reason you can't do some of both. Even if you are using a carbon canister, add a nitrate containing additive such as Refresh or Camco Ultra.

JamesG161 · Oct 10, 2018

Hold tank vents are just like Landlubber house sewer vents. Normally they are there for air intake and rarely for air out.
Activated charcoal can be reactivated, but it must be open and free to Vent the absorbed materials on "reheat"
____
Air OUT when your are "filling" you hold tank. So the filter would get odors.

Try putting the cartridge on a TWO WAY valve.
1) Valved OUT to normal vent air when OFF the boat
2) Valved IN when you are ON the boat.

Jim...

Peggie Hall HeadMistress · Oct 10, 2018

Chemical tank products may be "biodegradable," but they take quite a while to biodegrade and have a long half life too, doing a lot of harm to sea life meanwhile. Because they also kill bacteria needed to break down and emulsify solids, TP and all the other stuff that goes down sewer pipes on land, sewage treatment plants hate them. There are several products that work WITH nature to keep bacteria in the tank alive while still preventing odor. No-Flex Digestor Noflex Digestor is the best one today, but Odorlos Odorlos Holding Tank Treatment and Raritan K.O. Raritan maintenance products are also excellent products.

As for vent filters, I wish I could have invented a product that actually helps to create the very problem it’s sold to solve, because that’s what a vent line filter does. Filters do trap the gasses which try to escape through the vent line, but they impede the free exchange of air needed to prevent odor from forming in the first place, eliminating the need for a filter! What’s more, they only last about a year, are toast immediately if they get wet--which makes it impossible to backflush the vent line to prevent blockages--and ridiculously expensive. So install a vent line filter only as a last resort, because gasses that can’t easily pass through the vent line will go wherever they can-into hoses, eventually permeating even the best ones.

There's an entire section in my book that deals entirely with how to eliminate holding tank odor--odor out the vent. And another chapter that describes a very inexpensive simple modification to the flush water intake line that prevents odor from sea water left to sit and stagnate while the boat sits. I've posted a lot of that information over the years, but it's a whol bunch easier to find all of it in my book than it is to hunt through all my posts for it. You can order a printed copy from sbo.com (see link in my signature)...You can get the kindle edition from Amazon (you don't need the kindle reader....the kindle app can be downloaded to any Android or Apple phone or tablet). A lot of people get both--the printed copy to keep at home and the kindle to have on the tablet that goes to the boat.

--Peggie

thinwater · Oct 10, 2018

a. When I mentioned that formaldehyde was biodegradable, that was intended to be in the context of switching from formaldahyde to a bio-augmentaion formula. No special cleaning is required, just a few pump-outs with a little flush.
b. There are lots of goo formulations out there now, including those Peggy mentioned, those I mentioned, and more.
c. Curiously, the bio-products that work in holding tanks don't work for beans in portable toilets. Different geometry, different timing.

Yes, venting works. But I wish I could agree that vent filters don't work. But I can't. Installed properly, they can and do work trouble free for many years. First, they do regenerate to some extent insitu, lasting up to 5 years. This is observed fact, if properly installed. The reaction chemistry is well known and has been published many times. Back flushing the vent line and installing so they do not get wet is a matter of intelligent plumbing. Suffice to say, I never plugged a vent or had a filter get wet in 12 years of using one. On the other hand, if you simply cut the hose and install it near the tank, as many suggest... well, that won't work, and I'm sure that is what Peggy has seen, over and over. It is not that simple, though many suggest it it.

Overall, venting and using a bio-chemical is simpler and works better for most.

[Though I have less marine head experience, I do have decades with my boats and decades in refinery and waste engineering. Perhaps for me the vent filter was more science project than a practical solution... but t sure solved the problem, permanently.]

Benny17441 · Oct 10, 2018

jviss said:
Benny, you are completely missing the point. There is absolutely nothing wrong with the existing sanitation system.

Sorry, in all my years had never heard of anyone using charcoal filters for the head vent. From Peggie's explanation it seems like some medications, once you go on them you stay on them for life. I have had problems with odors but it seems I have always been able to resolve them by insuring the components are working as designed to work. I do use Raritan K.O. Good luck.

Stu Jackson · Oct 10, 2018

To save Peggie's tremendous volume of contributions, I've accumulated (pi!

) these (not really ten, either

). I also have her book, a wonderful gift from her personally, from a daysail we had together in April 2016 when I still lived in SF.

Peggie Hall's Top Ten Hits

Head Odors 101 http://c34.org/bbs/index.php/topic,5755.0.html

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

Head Leaks and Vented Loops 101.1.a http://c34.org/bbs/index.php/topic,5865.0.html

Head Odors 101.2 The Difference between KO & Odorlos (scroll up to Reply #2) http://forums.catalina.sailboatowners.com/showthread.php?p=890493&highlight=odorlos

Head Odors 101.3 Flix of New Vent http://c34.org/bbs/index.php/topic,8185.msg57288.html#msg57288

Head Hoses 101 http://c34.org/bbs/index.php/topic,5738.0.html

Head Pumps 101 Why just pouring water into the bowl is NOT a good idea http://c34.org/bbs/index.php/topic,5865.msg40604.html#msg40604

Fresh Water System Recommissioning 101 - Peggie Hall's "Cocktail" Rotten Egg Odor http://c34.org/bbs/index.php/topic,5836.0.html

PHII Installation with Photos http://c34.org/bbs/index.php/topic,3797.msg45617.html#msg45617

Ward H · Oct 10, 2018

A related question. If you flush with saltwater (marsh saltwater), then flush the toilet with fresh at the end of the day, you still can have a holding tank of decaying stuff that came in with the salt water.
Do the bio products control that smell as well? That was the smell we were getting out of the new 1" vent when we flushed.
We switched to fresh water flush and I flushed tank and started using Noflex Digester but was wondering if it worked on decaying organisms as well as human waste.

Peggie Hall HeadMistress · Oct 10, 2018

thinwater said:
But I wish I could agree that vent filters don't work. But I can't.

I've never said they don't work...they do. But they shouldn't be necessary except in installations that make it impossible to keep a tank aerobic...and while those are rare on most boats, I have run into a few boats over the years on which it was the only solution left...the last resort. They're also a bad idea on most monohull sailboats because the vent fitting on the tank is rarely in a location to prevent tank contents from spilling into the vent line and soaking it when the boat heels on that tack. And while DIY filters make them a lot more affordable than the brand name filters, it's still a PITA to have to keep replacing 'em. The typical re-routing of the vent line that's done to protect the filter only ends up making the filter necessary.

So while I don't deny that filters DO work, a couple of simple inexpensive modifications to the venting to allow enough air exchange with the gasses in the tank to keep it aerobic is a much better solution that works on MOST boats.
--Peggie

Davidasailor26 · Oct 10, 2018

I wonder if anyone has considered a hybrid approach with a Y valve to get the best of both worlds. Have a large straight through vent to provide oxygen for an aerobic environment. Then have a Y to reroute the vent through a filtered line and soak up odors when the head is in use. Might not be practical for livaboards but for people like @jviss who use the head only for a couple days then leave it for a week might it work?

thinwater · Oct 10, 2018

Peggie Hall HeadMistress said:
I've never said they don't work...they do. But they shouldn't be necessary except in installations that make it impossible to keep a tank aerobic...and while those are rare on most boats, I have run into a few boats over the years on which it was the only solution left...the last resort. They're also a bad idea on most monohull sailboats because the vent fitting on the tank is rarely in a location to prevent tank contents from spilling into the vent line and soaking it when the boat heels on that tack. And while DIY filters make them a lot more affordable than the brand name filters, it's still a PITA to have to keep replacing 'em. The typical re-routing of the vent line that's done to protect the filter only ends up making the filter necessary.

So while I don't deny that filters DO work, a couple of simple inexpensive modifications to the venting to allow enough air exchange with the gasses in the tank to keep it aerobic is a much better solution that works on MOST boats.
--Peggie

Yes, I agree with all of that. Simple is better!

JamesG161 · Oct 10, 2018

Davidasailor26 said:
I wonder if anyone has considered a hybrid approach with a Y valve to get the best of both worlds.

Well yes in my post#10 above.
Jim...

Peggie Hall HeadMistress · Oct 10, 2018

[

JamesG161 said:
Hold tank vents are just like Landlubber house sewer vents. Normally they are there for air intake and rarely for air out.
Activated charcoal can be reactivated, but it must be open and free to Vent the absorbed materials on "reheat"
Air OUT when your are "filling" you hold tank. So the filter would get odors.
Try putting the cartridge on a TWO WAY valve.
1) Valved OUT to normal vent air when OFF the boat
2) Valved IN when you are ON the boat.
Jim...

Tank vents have nothing in common with sewer vents. All tank vents--water, fuel and waste--have TWO primary functions--to provide an escape for air in the tank displaced by incoming material and provide a source of air to replace contents as they're drawn out of the tank. Sewage tank vents have a third function: to provide a unobstructed pathway for the free exchange of air with the gasses in the tank--to allow the tank to "breathe." When it can't, the environment in the tank becomes anaerobic...and it's only when organic matter breaks down in anaerobic conditions that it can generate stinky gasses--hydrogen sulfide and sulfur dioxide--and also methane, which is odorless but flammable. So a valve that only allows the tank to expel gasses would guarantee that those gasses would stink...and even gentle rocking would enough to push gasses out the vent while a boat sits, so you definitely want those gasses to be odorless...and a toilet flushing against a valve that only allowed air to come into a tank via the vent would pressurize the tank.

When organic matter breaks down in AEROBIC conditions it generates CO2, which is odorless, eliminating any need for a filter. And on most boats just swapping out the vent thru-hull for an open bulkhead thru-hull, replacing the 5/8" vent line with a 1" line (installing a new 1" tank fitting is easy to do, thanks to a li'l gizmo called the Uniseal UNISEAL ) and switching to a tank product that works with nature to assist in promoting the environment in which odor cannot occur is all that's necessary to get there.
--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein