Installing new through hull for holding tank breather

I am going to add a second breather to the holding tank to try and get some more air/oxygen into it to reduce the killer smell coming out the single vent when we flush.

It will be in the side of the hull, well above the water line, roughly half way between the water line and the gunnel. The hull is solid glass.

Question: Once I have drilled the hole with a hole cutter, is there anything I need to do to the hole before installing the fitting and sealing it with Sika?

BTW, the second breather will be fairly close to the existing one. I intend fitting a small scoop over one of them (facing away from the bow) the idea being to set up a small amount of suction which will hopefully draw air into the tank via the other breather, or act as a scoop if the wind is blowing the other way.

Since it is solid glass then sealing with Sikaflex is all you need to do. Does your second vent connect to the holding tank separate from the existing one? That is the best way to suck out the vent space.

But I would first increase the diameter of the existing vent hose. That is what Peggie- the Head Mistress, always recommends.

Also make sure that both vent hoses are routed uphill from the tank with no low spots.

David

You should round the outside edge of the hole in the hull so that the Sika will make an O ring around the through hull fitting.

All sealants have a limited life.

I would use a bit of Epoxy to seal the cut , then use your favorite goop.

Two vents on the same side, close to each other ? Doesn't make good sense. You really want the new vent on the opposite side of the boat so as to add cross ventilation. A breeze or the motion of the boat with both vents on the same side will merely "air block" the tank. Not serious but will not cause good ventilation.

Please rethink the new vent.

pete

Increasing the ventilation in the tank is the key to preventing odor, but I'm not crazy about the way you plan to do it. However, I need more information about the location of the tank and other details before I can recommend the best way to do it. So if you'd like to send me a PM that includes your email address (so we can move the conversation to email which is sooo much easier than PMs!) I'll be glad to help you sort out what to do to get the results you want.


--Peggie

Pete Meisinger said:

Two vents on the same side, close to each other ? Doesn't make good sense. You really want the new vent on the opposite side of the boat so as to add cross ventilation. A breeze or the motion of the boat with both vents on the same side will merely "air block" the tank. Not serious but will not cause good ventilation.

Please rethink the new vent.

pete

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Pete,

Your advice is good, but unfortunately the tank is located on one side of the ER and it is not feasible to run a line to the other side - it would have so many dips, twists and turns that it certainly wouldn`t be a straight uphill run to the outlet as the new one will, alongside the existing one - that's why I was putting the clam shell over one of them - to get a venturi effect - hopefully air being drawn out by that one.

Appreciate your concern though.

Could the second vent be on the same side but at opposite ends of the tank... fore & aft??? Instead of near or adjacent?

George, there was a "pong" around the tank in the ER 10 years ago, then I think it was a Lectrasan system. Hope it goes well.

Try and move the new vent so its forward of the parallel sides of the hull, then you will have forced air moving through the tank at anchor and underway. I used 1 1/2” sched 40 pvc pipe for all my poop plumbing. Both vents and piping.

More ventilation should work , but a small air pump might be less effort and is sure to work.

Try this first... put a filter on the air vent hose. They sell charcoal filters for this application. I did a DIY solution, by inserting a length of 1.5" PVC pipe filled with fish tank charcoal pellets. I did not glue the top cap so I can replace the charcoal every year or so. Since I have a fresh water electric head, the vented odor is not that bad, but a filter will minimize the odor.

Puffin_NT32 said:

Try this first... put a filter on the air vent hose. They sell charcoal filters for this application. I did a DIY solution, by inserting a length of 1.5" PVC pipe filled with fish tank charcoal pellets. I did not glue the top cap so I can replace the charcoal every year or so. Since I have a fresh water electric head, the vented odor is not that bad, but a filter will minimize the odor.

Click to expand...

Better to get adequate air in and have no odor to filter out
Filters ensure the tank will smell.

Bacchus said:

Better to get adequate air in and have no odor to filter out
Filters ensure the tank will smell.

Click to expand...

+1. No vent filters but add more air and the tank won’t smell.

HeadMistress said:

Increasing the ventilation in the tank is the key to preventing odor, but I'm not crazy about the way you plan to do it. However, I need more information about the location of the tank and other details before I can recommend the best way to do it. So if you'd like to send me a PM that includes your email address (so we can move the conversation to email which is sooo much easier than PMs!) I'll be glad to help you sort out what to do to get the results you want.


--Peggie

Click to expand...

This lady here, Peggie, knows her stuff on marine waste systems. She has a book specifically on dealing with waste systems and their problems. It's sold on amazon in any format you could want and very reasonably priced. Everyone that owns a boat with a head or toilet should have at least one copy. I recommend two, one for the boat and one to keep close at hand when dealing with head problems off the boat.


https://www.amazon.com/gp/product/1...23e60ae5abafa33beadc6a3ba67e56&language=en_US

Well, this post is getting a bit out-dated by now but I thought I would finish it off.

In summary, I had a horrendous smell coming from the holding tank via the breather - nothing inside. I only had a one 1inch ventline, no in line filter, which I had previously removed. Unfortunately it wasn`t physically possible to run a second ventline to the other side of the hull to gain more air into the tank via cross flow.

I considered a Groco bubbler but in the end, after discussions with the Headmistress, settled with using her "go to " additive (name escapes me at the moment) This worked well and got rid of the smell but was inconvenient as we don`t use the boat that often and I kept forgetting the additive.

So, back to my original plan - adding a second tank vent line, exiting the side of the hull right next to the original through hull vent BUT adding a small clam vent over one of them, facing aft.

Result, NO SMELL. I haven`t added anything for about three weeks, the tank has been pumped out several times and no smell - I even (weirdly so says my wife) went down to the engine room and took a cap off the tank - nothing.

So..........my cunning plan means that if the wind is blowing from forward, the clam generates a tiny amount of suction which is enough to suck air out of the tank and change enough to allow the good bugs (anaerobic?) to grow. With wind from aft it captures some wind and forces it into the tank and same same.

At the moment the clam is plastic (as an experiment) but now I am confident it works I shall change it the stainless.

So I am happy, as friends will be who are sitting in the aft deck when the head is flushed

Congrats and welcome to the camp of properly venting your holding tank and no smell.

Greetings,
Mr. B. The "good" bugs are aerobic. Meaning they make use of oxygen to break down the sewage. The way I remember the difference is aNaerobic has an "N" which means NO oxygen. Bad, stinky bugs.
Clever yet elegant solution.