Holding tank vent line

Is there any reason not to use the plastic accordion type hose called Bilgeflex*on the vent line to the thru hull? Seems it*would keep it's shape better in bends than the clear* tubing*usually used. It is not reccomended for below waterline thru hull, my vent discharges about 4' above the WL.

Steve W.


-- Edited by Steve on Saturday 25th of June 2011 08:26:07 AM

I don't think it is UV resistant, but other than that, that seems like it would work. *Sure hope so, because that's what we used to run the vent internally up to the top of the mast.

If it is inside the boat you still need to use a hose that will contain the smell

That is true. *We ran sanitary hose from the tank to the mast. *Good point.

Use sanitation hose--Shields or Trident #148 is adequate for vent lines and toilet intake lines--and straighten out the vent line to eliminate all the bends in it. To maintain the tank aerobically--which is the ONLY way to prevent odors-- vent lines should be straight as an arrow, at least 1" ID (1.5" is even better if the boat is big enough to allow a hole that large cosmetically)...be <5' long and rise no more than 45 degrees.* On* some boats that may require installing a new vent thru-hull.* Running a vent line up a mast actually creates the anaerobic condition in the tank that creates the odor you're sending up the mast to keep away from people....and also makes it impossible maintain the vent line to ensure that it never becomes blocked.

HeadMistress wrote:
Use sanitation hose--Shields or Trident #148 is adequate for vent lines and toilet intake lines--and straighten out the vent line to eliminate all the bends in it. To maintain the tank aerobically--which is the ONLY way to prevent odors-- vent lines should be straight as an arrow, at least 1" ID (1.5" is even better if the boat is big enough to allow a hole that large cosmetically)...be <5' long and rise no more than 45 degrees.* On* some boats that may require installing a new vent thru-hull.* Running a vent line up a mast actually creates the anaerobic condition in the tank that creates the odor you're sending up the mast to keep away from people....and also makes it impossible maintain the vent line to ensure that it never becomes blocked.

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*How could the length of the vent line have any measurable impact on anaerobic conditions in the tank? Anerobic bacteria thrive absent oxygen. *The vent, regardless of its length, would seem insufficient to oxygenate the tank, so anaerobic bacteria are going to thrive without some way of providing oxygen to suppress the stink causers. *What am I missing? *Is a bubbler not a better option than putting the vent line nose high? *

p.s. anaerobic or not, we have never detected the slightest whiff of odor from our system, although I haven't interviewed any seagulls flying overhead for their opinion. So there must be at least one other way to prevent odors.


-- Edited by Delfin on Monday 27th of June 2011 06:32:48 PM

The vent line has everything to do with creating AEROBIC conditions in the tank.... when it's short enough, straight enough, and of sufficient diameter to allow a free exchange of air with the gasses in the tank.* But the "standard" 5/8" ID vent line can't do that if it's more than about 18" long. A vertical line even that short cannot do that because the gasses in the tank are heavier than air they don't rise, fresh air doesn't fall, so the twain never meet. 5' is about the maximum length that will allow a tank to "breathe."

Aeration can indeed be an excellent solution to holding tank odor, but rarely needed in tanks smaller than about 40 gallons unless the tank location makes a short straight relatively horizontal vent line impossible.

So there must be at least one other way to prevent odors.

No, only ways to make 'em unnoticeable by filtering 'em or release 'em far enough away.* * When organic matter--ALL organic matter--breaks down ANaerobically, it always generates hydrogen sulfide and sulfur dioxide, which are not only very stinky, but also highly toxic...even lethal in high enough concentration...and also methane, which is also highly toxic AND flammable, but odorless.* But when organic matter--ALL organic matter, not just sewage--breaks down aerobically it always converts to CO2, which is both harmless and odorless.* That's just a law of physics.* But the only thing that matters is whether the way odor is dealt with on your boat makes you happy.

HeadMistress wrote:
The vent line has everything to do with creating AEROBIC conditions in the tank.... when it's short enough, straight enough, and of sufficient diameter to allow a free exchange of air with the gasses in the tank.* But the "standard" 5/8" ID vent line can't do that if it's more than about 18" long. A vertical line even that short cannot do that because the gasses in the tank are heavier than air they don't rise, fresh air doesn't fall, so the twain never meet. 5' is about the maximum length that will allow a tank to "breathe."

Aeration can indeed be an excellent solution to holding tank odor, but rarely needed in tanks smaller than about 40 gallons unless the tank location makes a short straight relatively horizontal vent line impossible.

So there must be at least one other way to prevent odors.

No, only ways to make 'em unnoticeable by filtering 'em or release 'em far enough away.* * When organic matter--ALL organic matter--breaks down ANaerobically, it always generates hydrogen sulfide and sulfur dioxide, which are not only very stinky, but also highly toxic...even lethal in high enough concentration...and also methane, which is also highly toxic AND flammable, but odorless.* But when organic matter--ALL organic matter, not just sewage--breaks down aerobically it always converts to CO2, which is both harmless and odorless.* That's just a law of physics.* But the only thing that matters is whether the way odor is dealt with on your boat makes you happy.

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With respect, the laws of physics would dictate that *if the gases in the tank are heavier than air it would be laregly immaterial*what the size or length of the vent was in terms of mixing outside air with those heavy gases and there will be little free exchange betweeen heavier than air gases down low, with fresh air whether 5' or 40' away. *

Imagine a 4" diameter vent at an ideal length of 48", absolutely straight. *Venting up through the saloon, say, at about boom height, just forward of the companionway. I'm guessing that you would want to hand out gas masks to guests for the cruise, and the idea of a 1" vent 40 feet up in the air would have a certain appeal. *

When you flush the loo, the volume of water will force that volume of whatever gases are in the tank out the vent. *Those gases are going to be discharged where you can smell them, or where you cannot. *I suppose if the diameter of the vent is greater, the gases will be mixed on discharge with a greater volume of air, but certainly not enough to avoid the gag reflex.

Without a way to vent those gases where you can't smell them, aerating the tank with a simple bubbler would seem more effective and simpler than providing for a large vent, whatever the length.*

I'm sure you know much more about this than I do...I've only been dealing with it for 26 years.

Delphin is absolutely correct on this one.*Blackwater treatment systems manufacturers*call for a vent line as high as possible and the literature for the type and size of systems installed on most smaller recreational boats makes no reference to vent filters or vent lines and fittings larger than 3/4 inch.

The idea that any kind of gas transfer through the vent line other than from tank to atmosphere might occur or is necessary for proper operation (other than during pumpout)*is ludicrous. In tanks which use a bubbler to provide air for digestion, the only stipulation is that the tank should not be "over pressurized" as they are only required to meet a test pressure of 7 feet of water column. Most of these larger units call for a 1.5 inch vent line and many of them use a vent fan located above the wheelhouse to ensure a good air flow out the mast vent.

A quick literature search of any of the major MSD manufacturer's sites will show that the vent line is certainly not used or required to function as a 2-way avenue for gas exchange.


-- Edited by RickB on Wednesday 29th of June 2011 08:18:21 AM

Oddly enough I've found thru the years that there is more than one way to do most anything. If you can appreciate the strengths and weaknesses of Corvettes and Mustangs you can probably see that there might be more than one way to vent a holding tank. If you are starting at ground zero and are looking for "a" way that works then go with whichever guru you want. If you have a current system that isn't working the way you want, then you can appreciate hearing about all the different methods there are which work with the pieces you already have. Henry Ford had a lot of great ideas, he wasn't the only person who knew how to make cars.

I had this great little ford *car back in the 70s** If I remember it was named after some* kinda bean

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Oddly enough I've found thru the years that there is more than one way to do most anything. If you can appreciate the strengths and weaknesses of Corvettes and Mustangs you can probably see that there might be more than one way to vent a holding tank. If you are starting at ground zero and are looking for "a" way that works then go with whichever guru you want. If you have a current system that isn't working the way you want, then you can appreciate hearing about all the different methods there are which work with the pieces you already have. Henry Ford had a lot of great ideas, he wasn't the only person who knew how to make cars.

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If you can appreciate the strengths and weaknesses of Corvettes and Mustangs you can probably see that there might be more than one way to vent a holding tank.

If your only goal is to provide an escape for air in the tank displaced by incoming contetns and a source of air to replace outgoing contents, there a dozen ways to do it. But very few ways to do it that provide enough oxygen to prevent the contents from becoming anaerobic, which is the only way to prevent odor.

Btw...a Mustang and Corvette have about as much in common as a Clydesdale and a Thoroughbred...both very fine horses, but hardly comparable.

I guess overall the Sweetank system would be the way to go.

Keith wrote:
I guess overall the Sweetank system would be the way to go.

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*Not necessarily... Whether a tank can be kept aerobic using passive ventilation or requires aeration depends on the size (mostly depth) and location of the tank.*

HeadMistress wrote:
If you can appreciate the strengths and weaknesses of Corvettes and Mustangs you can probably see that there might be more than one way to vent a holding tank.

Btw...a Mustang and Corvette have about as much in common as a Clydesdale and a Thoroughbred...both very fine horses, but hardly comparable.

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*I suppose it all depends how narrow your viewpoint is. I'd believe that most people would find many things which are similar (see definition of the word: comparable)*between the two horses and the two cars. If one was buying either they would weigh their own needs against the choices. Remember you wrote the word comparable, I said "appreciate the strengths and weaknesses" which is somewhat opposite of comparable or similar.

Both horses are capable of eating hay and making poop from it, that is a comparable item. Both horses can run around a track, both horses can pull a cart, but one can run faster and one can pull a heavier cart, those are strengths and weaknesses. Depending on ones needs one would buy one breed or the other, yes?

This is what most of us do with our waste systems. We weigh the cost, of tearing everything out and building what some expert deems a perfect system, versus making modifications to what*we have that fits our budget, needs*and skill level.

I guess if you followed the horse analogy you'd say that some of us pull a cart with a thoroughbred which on the surface appears to be wrong. But, if you widen your viewpoint, you'll see that silky racing is possible.

Ken

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Oh, I would pay GOOD money to see a Clydesdale pulling a sulky on a racetrack!

HeadMistress wrote:
Oh, I would pay GOOD money to see a Clydesdale pulling a sulky on a racetrack!

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*What if all of the horses on the track were Clydesdale's?* Or better yet the Clydesdale had one rider but every other sulky had four and were dragging a 200# block of concrete.* That Budweiser horse might do OK.

Peggie''
my vent is the standard 5/8'' with the charcoal filter When flushing the head it seems like a bigger vent would help When going bigger with the vent line what does one due for a vent filter? I have only seen the 5/8'' ones

You're a bad man motion30. (big smile)

2bucks wrote:
You're a bad man motion30. (big smile)

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* actually I am serious* that dam small vent filter why needed** causes my head not to flush well* and the charcoal is fresh

Deep six the filter, not needed. Peggie might tell you what to do with it but it could be painful.
Steve W

Sorry motion, Peggie rants against any kind of filter on a regular basis. I thought you were asking tongue in cheek.

Peggy is right to rant against filters on the vent line, They are a band aide and do nothing to deal with the smell inside the system which can eventually permeate the vessel. I have a live aboard friend who has lost his sense of smell, his visitors are few.

Well if I dump the filter I will no longer be able to raft with my friends on the weekend The filter really kills the smell I would love to be able to bring the vent line up to the fb and vent on top of the mast but surely no room for that

motion30 wrote:The filter really kills the smell I would love to be able to bring the vent line up to the fb and vent on top of the mast but surely no room for that

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*I see that Sealand sells a 1.5 inch filter. Install that somewhere accessible and run the largest tubing you can to the top of the mast and you should be good. A filter that size will take a while to clog.

Either that or take a length of PVC pipe as large as you like with a*threaded connector on one end and tubing fittings on each end so that you can refill it with charcoal or one of the other sewage filter media available online*and install that in the vent line. You just need sufficient volume of medium so that it won't clog up too rapidly. Being able to refill from bulk will save a fortune in media as well.

Think outside the Westmarine box ...

Surely you have room to run a 1/2 or 3/4 tube? If nothing else run*a hard pipe*external to the mast and mount it so it looks like it has always been there to serve some exotic maritime purpose.

Except for the fact that those tiny little filters are prone to clog very quickly, I can't imagine why anyone would object to having a vent filter installed. Most larger yachts have them as well as tank vent fans.*There is no reason any boat has to smell like a sewage treatment plant.

FWIW, last year I followed Peggy's advice.* Replaced the clogged 1/2" vent pipe with a 1.5" pipe.* Flushed the tank and charged it with the aerobic bacteria in the Raritan K.O. product.

Problem (enough stink to gag a maggot) solved!

*I have never seen the 1.5'' filter* I have modified the small filter so I can recharge it I was thinking about making a 1.5'' one* all the need parts can be purchased at home depot and the pet store

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*RickB wrote:
motion30 wrote:The filter really kills the smell I would love to be able to bring the vent line up to the fb and vent on top of the mast but surely no room for that

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*I see that Sealand sells a 1.5 inch filter. Install that somewhere accessible and run the largest tubing you can to the top of the mast and you should be good. A filter that size will take a while to clog.

Either that or take a length of PVC pipe as large as you like with a*threaded connector on one end and tubing fittings on each end so that you can refill it with charcoal or one of the other sewage filter media available online*and install that in the vent line. You just need sufficient volume of medium so that it won't clog up too rapidly. Being able to refill from bulk will save a fortune in media as well.

Think outside the Westmarine box ...

Surely you have room to run a 1/2 or 3/4 tube? If nothing else run*a hard pipe*external to the mast and mount it so it looks like it has always been there to serve some exotic maritime purpose.

Except for the fact that those tiny little filters are prone to clog very quickly, I can't imagine why anyone would object to having a vent filter installed. Most larger yachts have them as well as tank vent fans.*There is no reason any boat has to smell like a sewage treatment plant.

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RickB wrote:
Delphin is absolutely correct on this one.*Blackwater treatment systems manufacturers*call for a vent line as high as possible and the literature for the type and size of systems installed on most smaller recreational boats makes no reference to vent filters or vent lines and fittings larger than 3/4 inch.
-- Edited by RickB on Wednesday 29th of June 2011 08:18:21 AM

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*Interestingly, I just spent two weeks fighting this problem on a small cruise ship I sailed on as Chief Engineer.* As soon as I came aboard I noticed a really BAD smell.* The departing Chief told me he had been trying to solve the problem for a couple weeks with no success.* Clearly, there was a leak in the vent system, but where?* Sadly, it was at it's worst in the dining room of all places.* The first night I got up at midnight and pulled down lots of celing tiles but found nothing.* I traced the vent line from the tank, all the way to the top of the mast (35 feet up) and found no leaks.* Finally, someone mentioned the smell seemed to be coming from the AC vents.* What I found was the AC condensate drain had been connected directly to a tank vent.* When the departing Chief had replaced the air filters in front of the condensers, he used a thicker filter that in turn created a vacume on the drain line, sucking the yucky stuff into the vents.* I disconnected the drains and all seemed well, but the Captain was still quite nervous and wanted to make sure it was fixed.* So, when we docked at the next town, I got a smoke generator from the local fire department, and blew smoke down the vent line.* Since I had reconnected the drain line prior to the test, it quickly proved my theory correct when the smoke came billowing out of the AC vents in the dining room. Problem solved.* Oh yea, the escaping gas still stinks, but since the vent is at the top of the mast, no one ever notices...............Arctic Traveller *

One doesn't install a filter. If the larger vent line can't supply enough air exchange, an aeration system is the best solution...the Groco Sweetank system costs about the same amount as 3 filters.

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