Holding tank breather diameter

C

ColinR

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www.victoriashadow.co.uk
After thinking about it for years I'm finally biting the bullet and fitting a holding tank. Both Lee Sanitation and TekTank recommend 1 1/2" pipe for the breather. Problem is its too big to route anywhere but straight up through the side deck above the loo. This has two drawbacks; I don't make a habit of sailing with the lee rail under but it does happen and then the vent would be under water. And I don't want to cut any more big holes in the deck than I can help. One for the pump-out fitting is quite enough. On the other hand I could route a 3/4" pipe along under the toe rail to a spare anchor hawse pipe fitting on the foredeck and exit it there, keeping any bad smells as far as possible from the cockpit. I don't see why the pipe has to be such a big diameter as it is only a breather. Any ideas?

thanks

Colin
 
Hi There, I have a holding tank fitted in an SO37 and from memory the breather pipe is 3/4 in. Certainly not more than 1in. The tank itself is approx 50 litre capacity and it works well.

The breather pipe exits just under the deck thru the hull itself, not thru the deck. Its protected with a standard scoup fitting on the outside of the hull and its not comprimised when well heeled. The only fitting connected from directly overhead the tank is a fitting similiar to a water or diesel fitting used only to drain tank (by suction) in the event of a major blockage !.

I dont believe anything more that 3/4 in. is required. The only real effect I can see is the rate of discharge, but thats not a big issue.
 
I.5 " is certainly the recomended size for a holding tank vent.

It used to be less on the BWB inland spec but was increased to the current size a few years ago.

I had a similar problem as you and ended up taking the vent pipe up as high as possible inside the saloon then back down to the outlet.

I also have a carbon no smell filter in the line and use 1 1/2 inch pipes.
 
1 and a 1/2 pipe in when pumped in flow has to out flow has to match inflow .

as to lee rail problem erm dont know ... could it be a snorkel on the end ?
 
The 38mm vent on my holding tank exits under the toe rail on the stern quarter where it won't get wet. The reason this size is recommended is to allow sufficient vent for the when the tank is emptied by a pump out - to stop the tank imploding. All the hoses on the tank are 38mm.
 
I have 25mm on mine. On one boat it exits through the coachroof side with a scoop cover. On the other just through the hull beneath the toe rail. You can put a soop cover on it if you want but don't think there will be a problem - or take the pipe up through a loop above thedeck level internally.
 
1 and a 1/2 pipe in when pumped in flow has to out flow has to match inflow
Click to expand...
you do not need anything like as large a vent as inlet pipe to allow air to escape.

Large enough to prevent implosion when emptying by pump-out perhaps the important the consideration
 
VicS said:
you do not need anything like as large a vent as inlet pipe to allow air to escape.

Large enough to prevent implosion when emptying by pump-out perhaps the important the consideration
Click to expand...


i was kinda meaning that but was talking to swmbo about going sailing after xmas so was distracted ..:o also if a carbon filter in vent restricting air flow would add to implosion risk specially if the pipe was too small!
 
We too followed the industry recommendation and fitted (with a struggle) a 38mm vent, to match the inlet; we've since met innumerable yachts with smaller 25mm and even 13mm vents who've had no problems at all. having read the posts, I do wonder if dock-side pump-outs might cause a problem, but you'll probably need to sail to the USA to find one.

If I ever install another tank, I would probably install a 19mm vent pipe, which would not only be much cheaper, but it'd also be feasible to route it all the way from the heads to exit through the transom. The worst of the smell from holding tanks occurs when the toilet is being pumped and displaced gasses exit the vent and waft gently across the cockpit, by exhausting the vent through the transom, this smell would be downwind.
 
VicS said:
you do not need anything like as large a vent as inlet pipe to allow air to escape.

Large enough to prevent implosion when emptying by pump-out perhaps the important the consideration
Click to expand...

Search back for posts by 'Headmistress' (Peggy Hall).....

The reason for the 38mm vent recommendation is to keep the tank well ventillated to encourage aerobic bacteria and discourage anaerobic bacteria.

Anaerobic bacteria are the ones that make the tank contents stink. If it is kept in an aerobic condition, then there is no smell.

(That said, our tank has a 25mm breather. No problems or smells but it's a direct ~2' run).

Andy
 
misterg said:
388 posts

Just need sorting :)

(Either option works)

Andy
Click to expand...

Ah I only found threads she had started! :( "Find all posts" from her profile will actually find 500. (I did not count how many Google found)

As she no longer posts on here its good of you to offer to sort them all.
It'll make a valuable resource .
 
misterg said:
Search back for posts by 'Headmistress' (Peggy Hall).....

The reason for the 38mm vent recommendation is to keep the tank well ventillated to encourage aerobic bacteria and discourage anaerobic bacteria.

Anaerobic bacteria are the ones that make the tank contents stink. If it is kept in an aerobic condition, then there is no smell.

(That said, our tank has a 25mm breather. No problems or smells but it's a direct ~2' run).

Andy
Click to expand...

I agree with Andy 100% read the Heads Mistress, Peggy Hall's book "Fact vs. Folklore". I know what a smelly boat is like, and you would not want that.

Goerge
 
Agree with above about aerobic (sweet) and anaerobic (stink) decomposition. I put a Tec-tank holding tank into a forecabin locker and attached a big vent. This goes up to and along the ceiling, and then out through a skin fitting about a metre back from the stem. Seacock attached in case of heavy seas. Never had a problem with smell.
 
BobnLesley said:
The worst of the smell from holding tanks occurs when the toilet is being pumped and displaced gasses exit the vent and waft gently across the cockpit, by exhausting the vent through the transom, this smell would be downwind.
Click to expand...

A certain lady made a living out of solving this problem when it first became apparent when holding tanks became a feature of boats in the USA . Always new when a movement had taken place as the evidence wafted across the aft deck.

One necessity required to help in the anti pong battle was as large an air vent as possible to try and get those aerobic bugs fit and healthy and kill off the anaerobic bugs. It seems that with short run large diameter vents this was possible. Mind you if you do have the evidence wafting over the after deck every time the superloo is used then there is help available which was even approved by our Headmistress.

Do a Google for Oderlos and you will find it available in all sorts of places included those emporiums you love to hate.


http://www.mailspeedmarine.com/toilet-systems/jabsco/odorlos1262043.bhtml


It is not Snake Oil and believe it or not Swimbo may even thank you for adding this to your system and making life after flush more pleasant.



PS our Headmistress is alive and well and holds court in various locations in the USA as well as enjoying another new hobby...:)
 
If the concern is the tank collapsing when pumping out, Vetus do a Vacuum Operated Vent Valve (VRF56A) which will open if there is too much vacuum in the tank.

(Can you have too much vacuum ?)

J
 
Last gasp at this potential smelly problem.

The tank is gravity operated effectively. To dump tank you simply open the large outlet valve and bombs away... to cause it to implode a high level of vacuum needs to be applied and the tank sealed for this to happen.

If the breather is blocked it simply stops working...only a partial discharge.

If the breather is too small in diameter it just takes longer to empty.

As regards smells, remember when the tank is being dumped air is drawn in through the breather pipe, not out.. however if the tank is full it will most definately smell and this will come from the breather pipe..

Also most important the tank needs to be dumped as often as possible rather than leaving the bacteria do its trick...

I try to empty it each time before returing to the berth and also flush it thru regularly with soapy freah water and there ends the problem with tanks, breathers, smells etc...
 
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