# Fresh water tank vent location options



## josrulz (Oct 15, 2006)

Hi all,
I tried searching on this, and just couldn't find results amidst all the threads on holding tanks, vents, etc. If there's a link or something that I should read, please let me know. 

On our 1984 Sabre 34, we have two fresh water tanks under each settee. Each has a vent line that runs forward, where they are T'd together under the V-berth, and then vented into the anchor locker.

I may need to move that anchor locker vent location due to some modifications in that area, and I'm wondering if I can choose a different location for the fresh water vent. Are there other options? Best practices for freshwater vent location and/or design? Other common locations on monohulls (if it differs on catamarans)? 

I looked through most of the books I own, and the best I cold find was that there should be vents, and that's about it. Any thoughts on this?
Thanks,
J


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## remetau (Jan 27, 2009)

Our tanks vent to our galley sink.


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## josrulz (Oct 15, 2006)

remetau said:


> Our tanks vent to our galley sink.


Thanks remetau, can you be a little more specific about the fixture? Sorry--I'm not familiar with that set-up, though I've heard reference to it.


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## Sabreman (Sep 23, 2006)

Could you put in a T fitting to the sink drain?

Boat looks good, Jim.


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## josrulz (Oct 15, 2006)

Thanks Sabreman. 

Wouldn't T-ing it to the sink drain risk contamination of the tanks? Perhaps I'm not getting it.


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## mitiempo (Sep 19, 2008)

Don't put the vent into the sink drain. It will contaminate the tank.

Some boats vent to the sink like shown below (older Swan). The other option is high in the boat near the tanks, ideally on center. When filling water will come out the manual water outlets at the sinks first as they are lower than the vent. Inside vents avoid salt water contamination.


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## remetau (Jan 27, 2009)

Yes, my vent is much like the one in the picture above.


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## sailingdog (Mar 19, 2006)

Venting the tank inside the boat makes a lot more sense than venting it externally. Putting a freshwater tank vent on the hull is just asking for contamination, especially if you dip the rails when sailing.  Venting them to a fixture mounted above the galley sink makes sense so that any water that does come out drains out the sink.


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## Sabreman (Sep 23, 2006)

All the descriptions make sense, but now _I'm_ confused. Like josrulz, my vent is in the anchor well which definitely gets wet. While quite a bit higher than the tanks and faucets, I now wonder why I don't receive any contamination. Perhaps the vent is a one-way valve. That's the only explanation that makes sense to me.


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## mitiempo (Sep 19, 2008)

It is designed to vent air, not water. I doubt it is a one way valve.


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## josrulz (Oct 15, 2006)

Sabreman said:


> All the descriptions make sense, but now _I'm_ confused. Like josrulz, my vent is in the anchor well which definitely gets wet. While quite a bit higher than the tanks and faucets, I now wonder why I don't receive any contamination. Perhaps the vent is a one-way valve. That's the only explanation that makes sense to me.


Hi Sabreman, if your set up is like mine (good chance it is), the vent is like a holding tank vent high on the bulkhead of the anchor locker. Although the locker gets wet inside, the vent is aimed down, so to get sea water in it, the anchor locker would have to literally fill up.

I don't know if I'm going to re-run it, but if I do, I like the sink location idea. 
-J


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## mgmhead (Jan 14, 2007)

Jos,

My two tanks each have their own vent. The vent hoses are led to a thru-hull vent located just below the toerail. Port to port and starboard to starboard, naturally, and positioned roughly below the fresh water deck fill. The same for the holding tank, a vent of its own located just under the toerail on the port side.

Works great.


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## RichH (Jul 10, 2000)

In most 'sanitary' systems the vent discharges to the HIGHEST part of the system ..... and is protected by a 'bio-blocking' filter. This is to protect the entire system from aspiration of biological spores, spores that are bacterial, or fungal. Mildew (fungal) spores are the most prevalent contamination to a boat's water tankage, many of these are very toxic or dangerous especially to one with a weakened immune system.

The vent filter can be a commercial/industrial 'capsule' filter made from hydrophobic/teflonic membrane @ 0,2µM (100% - absolute) retention and approx. 1-2 sq. ft. surface area and mwith 3/8 or 1/2" hose barb connectors. These are available from those filter suppliers/distributors who serve the bio-pharm industry. Approx. $75-100 ea.
If thats too much $$$ then take a fist sized 'wad' of bandage cotton placed over the terminal end of the vent tube, cover with bandage gauze, and tape in place. Keep dry and change every 6-12 months. The vent filter is always at the 'highest' elevation in the entire system. 

Suggest you inspect and visualize the vent line 'all-the-way-to-the-tank'. 99% of the time such an unprotected vent line will contain massive colonies of bacteria/mold/mildew, etc. .... and 99% of the time this is why your tank eventually become totally fouled with biological growth. Typically if the vent hasnt been protected it usually needs replacement if not 'totally' free of discoloration/growth. To a microbiologist, most boat water tank 'vent systems are cause for projectile vomiting. 
;-)


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## Sabreman (Sep 23, 2006)

> Suggest you inspect and visualize the vent line 'all-the-way-to-the-tank'. 99% of the time such an unprotected vent line will contain massive colonies of bacteria/mold/mildew, etc.


Excellent idea.

I like the sink location too.


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## RichH (Jul 10, 2000)

Sabreman said:


> I like the sink location too.


Not a good idea, too close to 'food, etc. contamination' and the bacteria, etc. then enter the tankage by 'retrograde' movement from the 'sink' area TO the tank.

If you had a portable drinking water container, would you leave the lid off or keep it in/near your 'sink'? Dont think so once you saw or realized the quickly growing bacteria colonies (slime) that form on the inside walls of the container.


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## SemperLiberi (Dec 27, 2008)

Rich,

I was reading forums on how to keep water tanks clean and came across your suggestion here to put a hydrophobic vent filter on the tank vent line. That makes a lot of sense.

I've searched extensively for this product and it's hard to find. There's a whole class of vent filters for the lab market (Pall Acro 50, Millipore Aervent), but their filter size is way below the 1-2 ft^2 you recommended (20 cm^2). One claims 27L/min air flow, which seems marginal assuming say, a ~5 gpm fill if I've done my math right.

The only filters I've found larger seem to be aimed at massive tanks for the beverage industry and cost in the thousands. I'd consider up to about $100. Any suggestions for brand / model / where to buy?

Thanks!
- Craig


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## RichH (Jul 10, 2000)

What you want is slightly larger than the 50mm. Pall, Millipore, Parker Advanced, Meissner, Whatman, etc. all make 'capsules' of 1 sq. ft. of membrane surface area ... abut "fist" sized and come with hose barb connectors. Suggest you contact a 'distributor' not 'direct w/ mfgr' and sweet talk them into omitting the minimum charges / minimum qty, etc. that usually apply. Also you dont need a 'sterile' system filter, just a 'log reduction' value (LRV) @ 0,2µM, hydrophobic teflon or equivalent membrane. an example: Single-Use Capsule Filters - Meissner Filtration Products

Failing to obtain one from an ethical mfg., just take a fist sized wad of loose bandage cotton held in place with bandage gauze and a minimum of bandage tape to hold in place on a hose end; keep dry and change-out at least every 12 months. That will keep all the 'spores' out of the tank ... but tank, vent and distribution lines, etc. still needs to be 'shock sanitized' yearly with clorox, etc . at ~40 oz. clorox per 100 gallons for 1-2 hours. 
When you open the tank's inspection port, reach in and feel 'slimey stuff' (bacteria, etc.) on the tank walls, then you need to 'scrub out' the tank, etc. before sanitizing. 
;-)


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## Skipper Jer (Aug 26, 2008)

Is there any reason one could not use say a 1 micron 10" standard sediment water filter instead of these "capsule filters"? The same kind of filter used in under the sink filters for water consumption? Yes one would have to add some adapters to the filter housing but the advantage is standard filter, reasonable cost and available at big box stores.


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## SkywalkerII (Feb 20, 2008)

My Tartan 27's fresh water tank vents inside the anchor locker, FWIW.

SKywalker


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## SuperV (Jul 5, 2014)

I know that the original thread is from 2010, but since it was warmed up I came across it and don't think I saw in any of the replies a mention of a bend to allow venting overboard. Granted, venting inboard is best, but if I have a bend that brings the hose up as high as possible under the deck, I would think that should suffice. I never thought about a bio filter on that line. How is that different from air that gets into the system from other sources (e.g., while repairing stuff)? I always though it would be enough to add chlorine to the tank while filling after an initial shock treatment.


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## Skipper Jer (Aug 26, 2008)

"I never thought about a bio filter on that line. How is that different from air that gets into the system from other sources (e.g., while repairing stuff)? I always though it would be enough to add chlorine to the tank while filling after an initial shock treatment.
"
Good point about air getting into the system from other sources. Maybe, this is a WAG, with all the sloshing around from sailing to weather the chlorine evaporates leaving the water prone to infection. Not to crazy about venting over board. Might let sea water into the tanks.


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## mitiempo (Sep 19, 2008)

Vent inside. Sediment filter everything going into the tank. High quality filter before use at the galley taps.


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## pdqaltair (Nov 14, 2008)

The plumbing code calls for 16 mesh filters on portable water storage tanks. The point is to keep out larger debris and bugs. I bet a few are crawling in there, specifically mosquitos. All you need to solve this is the cheapest Shurflo strainer.










The tank is never going to be sterile (impractical to filter that slow at the dock), so 16 mesh + a no-seawater location seems practical. Inboard vs. overboard? I think that depends on the specific geometry. Mine is over board, and since it is also an overflow, it works fine. But it is a boat-specific solution (the vent opens down, through the bridge deck).


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## RichH (Jul 10, 2000)

Captainmeme said:


> Is there any reason one could not use say a 1 micron 10" standard sediment water filter instead of these "capsule filters"? The same kind of filter used in under the sink filters for water consumption? Yes one would have to add some adapters to the filter housing but the advantage is standard filter, reasonable cost and available at big box stores.


Some very good reasons for not relying on variable µM and non-hydrophobic filters in a vent line from a 'big box store'.

Such filters are not 'hydrophobic' ... a filter used in gaseous service (vents are 'gas' service) will seriously degrade in µM retention ability if it becomes 'wetted'. Hydrophobic membranes dont become wetted per se and therefore dont lose their µM retention because the filter media remains 'dry' or become totally 'blocked' (no gas flow) when wetted.
As an example, a hydrophillic (wettable) filter rated at ~0,5µM (gas rating) will be only able to retain ~5,0µM or greater when the filter media becomes wetted ... about a magnitude less in retention, meaning that all/many of those particles already captured will be released when the filter media gets 'wet'.

Big Box stores dont sell/offer hydrophobic filters; plus, the 'liquid' filters they do sell are very variable in the advertised µM 'rating'. These filters are NOMINALLY rated, meaning that their efficiency of capture at their 'rating' may be between only 50% to 90% of particles captured at that 'rating'. And, the housings used are either flat gasketed or 'knife edge seal' (filter-to-housing) which is incompatible for reliably retaining particles at much less than ~5µM .... such particles can usually easily 'bypass' through the flat gasket area. Once one needs to filter below 5µM (liquid) double O-rings in a 'piston seal' housing are needed to prevent such 'bypass'. For a vent you need very high efficiency of retention for both the filter _AND_ the housing, as one or a few 'living' particles that bypass can easily morph into a large 'colony' if they 'get through'.

Summary .. the big box store stuff is very low technology and a lot of it is 'cheap junk'; but, is OK for crude RE-filtering of 'drinking water' .... or, for retaining waterborne pathogenic CYSTS (oocysts) _but if and only if_ the oocyst filter cartridge has a listed 'retention validity claim': "99.99% retention of oocysts", etc.

Also FWIW .... that 16 mesh plumbers code is obsolete especially in areas that have a high potential of chlorine resistant oocyst contamination. It would remain applicable only for well water sources or in municipal systems (drawing from surface water) that have been 'updated' to coarse RO --> 1,2µM (99.99%) post treatment.


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## Skipper Jer (Aug 26, 2008)

Thanks RichH. Because of your explanation I won't be wasting effort, time and money installing a sediment filter on the fresh water vent line.


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## RichH (Jul 10, 2000)

Suggestion - put a run of small diameter (3/8-1/2" dia) tubing from the TOP of the tank into one of the 'highest' levels inside your cabin, terminating near the 'coachroof' (inside a hanging locker works best). Take a fist sized wad of 'freshly opened' bandage cotton fluff and place it (loosely) on the end of the open tube, cover this with 'bandage gauze' and 'tape' to hold in place and allow free flow of air. Keep it DRY and change out every 6-12 months. Cost: about $6 plus tubing.
.... then, Disconnect / block / remove the fungus/bacteria filled OEM 'vent'


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## Puddin'_Tain (Feb 14, 2014)

I realize that this isn't a solution for everyone, but here is how I handle water storage on my 27' boat.

I have a 20 gal tank under the aft end of the v-berth that is vented via a small diameter tube (which I should probably replace, as its pretty nasty-looking) to the anchor locker. Since the boat gets weekend use (at best), the tank and associated plumbing are basically just a big microbiology culturing experiment as far as I'm concerned (although, I do add a slash of Clorox whenever I fill the tank so the water is probably safe to drink, if somewhat unpalatable). So, I use the water in the tank for washing purposes only, and stock several 2.5 gal carboys of "Spring Water" from the grocery store as drinking and cooking water. We also usually carry a case or two of individually sized water bottles and plenty of other bottled drinks. Even on a week-long coastal cruise with two adults and two teenagers (yes, a 27' boat gets pretty crowded under such circumstances), such an arrangement seems to work just fine.


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## Philzy3985 (Oct 20, 2012)

I guess for the sake of varying answers, I'll chime in.

On my Catalina 30, the fresh water tank(s) vent together up through a stanchion, and out a small hole drilled through the side of the stanchion into the stem. My guess is that the particular stanchion was designed for that, or there's a small vent on the deck, which the hollow stanchion was placed above.

Anyway, they probably did that over 6,000 times while making that boat and other Catalina's, so it must have a good reason.

Such a beamy boat, I've never been close to burying the stanchion that deep on a heel.

Also it's worth mentioning that I don't drink the tank water, just use it for cleaning my hands and dishes, occasionally to brush me teeth. Being almost 30 years old, I'm sure there's stuff in there, marinating, that I don't want in me.


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