Holding tank vent filter

[DArcy]

I am tracing plumbing in my new boat and came across a "big orange filter" in the vent line Big Orange


This boat has fairly bad head smell so one of my first projects is to sort that out, starting with new hoses.
Do filters in the vent line help or hinder boat smells?

 

[dlochner]

@Peggie Hall HeadMistress will tell you that they are good for the manufacturer's profit, not so good for holding tank smell. The filters are prone to clogging, which causes other issues besides odor.

 

[Justin_NSA]

That hose is tiny. Easy for critters to clog too.

 

[DArcy]

It is 5/8" hose. I'm on the boat right now and don't have Peggie's book with me. I don't recall what she recommends for vent hose size.
It seems like the filter is just a restriction in the vent line and I remember reading in the book about promoting aerobic decomposition to eliminate smells which would need good ventilation

 

[Mr Fox]

If I remember correctly, Peggie recommends against any vent filters, and at least 3/4" vent line, going to a mushroom vent, with no screens in the way. The vent is there to equalize pressure when you pump things in or out of the tank, so the size is about ease of keeping it unclogged. The no filter is about keeping it unclogged (cause they clog when wet). The mushroom vent, or at least no screen on the end is about keeping it unclogged.

I think (and maybe she will weigh in) that the vent is not actually about providing enough air to keep the tank's contents from smelling. The tank is rarely the source of the smell inside the boat because it effectively contains the smell. Odor is typically from permeated hoses, so looks like you are on the right track with replacing the hoses.

 

[dlochner]

It is 5/8" hose. I'm on the boat right now and don't have Peggie's book with me. I don't recall what she recommends for vent hose size.
It seems like the filter is just a restriction in the vent line and I remember reading in the book about promoting aerobic decomposition to eliminate smells which would need good ventilation

you have a good memory.

At least ¾", preferably 1" vent hose. No need to remove the other hose more air is better.

 

[DArcy]

I'm thinking about moving the vent. It is about 1 inch from the water tank vent. Seems like a bad place for it, could easily be moved a few feet forward which would make the vent line shorter.

 

[Justin_NSA]

I'm thinking about moving the vent. It is about 1 inch from the water tank vent. Seems like a bad place for it, could easily be moved a few feet forward which would make the vent line shorter.

That was an odd positioning choice. I'd weigh that against a new hole though.

 

[dlochner]

I'm thinking about moving the vent. It is about 1 inch from the water tank vent. Seems like a bad place for it, could easily be moved a few feet forward which would make the vent line shorter.

If the water tank vent is outside the boat, I'd move the water tank vent. The vent should be in a well protected place to reduce the chance of contamination. One of my tanks vents into the anchor locker, the other vents into the bilge. This vent has a loop in it and then drains into a larger hose that runs into the bilge.

 

[Peggie Hall HeadMistress]

Y'all not only have my book, you've actually read it...I'm impressed!
You're quite right that I don't recommend holding tank vent line filters, especially on sailboats 'cuz the filters are toast immediately if they get wet and heeling can often send tank contents into the vent line.

I wouldn't worry too much about the close proximity of the waste and water tank thru-hulls...the type of thru-hull boat builders use on all tank vents are designed to keep sea water and any other contaminants out. But I like the idea of moving the vent line forward anyway...the shorter and straighter the better. Where is the tank located in the boat?
If you want to increase it to 1" you'll have put a new 1" vent fitting in the tank--actually pretty easy to do, thanks to a li'l gizmo called the Uniseal UNISEAL --and of course the vent thru-hull has to be 1" and also be an open bulkhead or "mushroom" thru-hull.

Make sure the hoses are the source of your odor inside the boat before jumping to replace 'em. If it's been a while (never?) since you really CLEANED the bilge instead of just dumping some bilge cleaner and water into it and calling it done, it could be the culprit, 'cuz a wet dirty bilge is a primordial soup that can make a whole boat smell like a swamp or even a sewer. So do the "hot wet rag" test on the hoses.

More later...I have to be somewhere 10 minutes ago!

--Peggie

 

[Ron20324]

It is seldom mentioned when considering a vent (or any hose/fitting) if you use a 5/8 hose and put it on a fitting of any type, you are putting a restriction in the vent. IIRC, if using a hose with , say, 2 inch I.D., doubling the I.D. gives you FOUR times the original I.D. area.

 

[dlochner]

You are correct. The area of a circle is π r^2. So a 1" ID hose has an area of .785 square inches, π * (.5)^2. A 2" ID hose has an area of 3.14 square inches, π * (1)^2.

 

[RoyS]

Although Peggy does not like vent filters, they do in fact work. When you flush the toilet, air in the holding tank is forced out. If that is when you notice the odor, replace or recharge the vent filter. Some vent filters may be recharged with activated charcoal. I get activated charcoal from the pet store tropical fish department.

 

[Peggie Hall HeadMistress]

Vent filters don't PREVENT odor out the vent, they just block it. IOW, they actually help to create the problem they're sold to solve. Increasing the ventilation and using a tank product that doesn't just add a chemical odor to the sewage odor prevents odor out the vent, making filters unnecessary.

--Peggie