Screens in holding tank vents

[sailingharry]

So, I have two holding tank vents. And neither work! I'm digging into it. The first vent fitting I removed had a screen in each of two 1/4"(3/8"?) diameter holes. One is no longer in its proper place (it's inside the fitting). I've cleaned everything out, removed the retaining ring, and rescued the screen. Unfortunately, the screen is deformed and will no longer stay in the hole.


I realize that the screens keep out bugs that like to make homes. But they also substantially reduce air flow.


Am I better off with out it (and should I remove the other)?


If I need the screen, is there a source for these little stainless screens, or do I need to buy a whole new vent fitting?


As an aside, this fitting is smaller than the hose. The hose clamps have squeezed down on it, but it is still the small point in the vents (I do have port and starboard vents). What is the best vent fitting to use -- and is this a good time to upgrade?



Thanks for thoughts. And special thanks if Peggy answers!

[rslifkin]

Remove the screens. They're good for water or fuel tank vents where you want to keep bugs out. But for a holding tank they're just a needless flow restriction. For a holding tank vent, any plain through hull fitting will work.

[mottseng]

Originally Posted by rslifkin

Remove the screens. They're good for water or fuel tank vents where you want to keep bugs out. But for a holding tank they're just a needless flow restriction. For a holding tank vent, any plain through hull fitting will work.

Totally agree !!!

I increased my vent to 1" and installed a new vent fitting without screen. (Peggy recommended).

[JoeRobertJr]

I'd lean towards keeping a screen to discourage insects like mud wasps from completely plugging up the vent line with their home. I suspect you could make your own by cutting any common plastic screen material into a small circle, and then shaping it into a cone, pushing it apex in.

[sailingharry]

Originally Posted by mottseng

Totally agree !!!

I increased my vent to 1" and installed a new vent fitting without screen. (Peggy recommended).

Yes, it seems her recommendation is a standard mushroom thru-hull. My hoses are 3/4" and they make a variety of white "plastic" 90 degree versions for $10 or so. If you trust "plastic." While my vents are within an inch or so of the toe rail, they are just a bit forward of amidships. We really hate to bury the rail -- but it does happen. The small vents minimize the inflow. Perhaps a large vent will encourage me to make it happen less often (the admiral would like that!).

[Jammer]

Originally Posted by sailingharry

Am I better off with out it (and should I remove the other)?

Probably. Peggy recommends using vent fittings without screens. I have screens on the holding tank vent on my boat, and have not found them to be a source of trouble.

If I need the screen, is there a source for these little stainless screens, or do I need to buy a whole new vent fitting?

You can buy 12" square sheets of screen material at McMaster-Carr and cut them to size with a punch.


https://www.mcmaster.com/products/screens/


https://www.mcmaster.com/products/le...ole-punches-7/

You may find that it's cheaper to replace the assembly however:


https://www.fisheriessupply.com/sea-...-vent/352110-1

[capt jgw]

I would have said to remove the screens, but where we're at now north of St Louis MO we're inundated with mud wasps. Every time I open a locker or something I find a new nest. They love crawling into holes and building in there. So if mud wasps are common in your locale you might want to leave them in. Just be real careful not to overfill your tank cause the screens almost guarantee the vent will clog.

[markxengineerin]

Yes, I've had mud wasps set up shop in my holding tank (and every other) vent. A larger size vent might fix that problem, but my solution for now is to put a piece of masking tape over the vent when I'm on the hard. Any pressure difference will easily dislodge the tape enough to flow/equalize, still block the wasps, and I'm not using the head on the hard. Remove tape when back in the water. I do wish there was a better solution that retained the original small/good looking bronze thru hull vents.

[peghall]

Screens become clogged by pollen and dust and also rust if the screen is metal. An open thru-hull has two advantages 1. allows a lot more air exchange with the gasses in the tank, which is necessary to prevent odor from forming. 2. makes it possible to prevent vent line blockages by putting a hose nozzle against it to backflush the vent line every time you wash the boat and/or pump out or more often if necessary to keep the vent open. However that's not possible if there's a filter in the vent line because vent filters are "toast" immediately if they get wet 'cuz the charcoal swells and blocks the vent line...something that can happen due to heeling, which makes vent line filters a bad idea on sailboats anyway.

Fwiw, I'm very familiar with "dirt wasps" (aka mud or dirt daubers)...fought 'em for years, but they're mostly active in the spring building their nests to lay their eggs. Back flushing the vent line will give their nests a water slide ride into the tank.

--Peggie

[sailingharry]

So, I'm settled on new mushroom tru-hulls as a better answer than what's in there.


The existing were about an inch in diameter in chrome. Even though they were up high (just an inch below the toe rail), they were fairly small and inconspicuous. The new ones will be over twice the size. Stainless/chrome would look OK, but white would be best. It's not really a price issue -- Groco is the top at $40, solid stainless can be found for under $30, and most plastics are around $20 (some plastics are more than some stainless!).



Problem is material. Plastic comes in nylon and polypropylene, some with fiberglass reinforcement. Maerelon is also an option (but not in a 90, so that's a problem), but only comes in black.


So, are there any white plastics that are suitable for above waterline use? I know some are very bad, but I know some seem to last a long time. My little bow rider has a 20 year old white plastic discharge for the bilge pump that "seems" to be good.

[capt jgw]

Originally Posted by sailingharry

So, I'm settled on new mushroom tru-hulls as a better answer than what's in there.


The existing were about an inch in diameter in chrome. Even though they were up high (just an inch below the toe rail), they were fairly small and inconspicuous. The new ones will be over twice the size. Stainless/chrome would look OK, but white would be best. It's not really a price issue -- Groco is the top at $40, solid stainless can be found for under $30, and most plastics are around $20 (some plastics are more than some stainless!).



Problem is material. Plastic comes in nylon and polypropylene, some with fiberglass reinforcement. Maerelon is also an option (but not in a 90, so that's a problem), but only comes in black.


So, are there any white plastics that are suitable for above waterline use? I know some are very bad, but I know some seem to last a long time. My little bow rider has a 20 year old white plastic discharge for the bilge pump that "seems" to be good.

I wouldn't trust white plastic near or below the water line, but up just under the toerail? What's the worst that could happen with that? Not much. Marelon is the best for plastic, if you wanted it white I bet you could paint it and it would last at least a few years before you had to touch it up.

[Jammer]

Stainless can be sanded and painted. Just saying.

[Knotical]

Harry, first year we bought the boat I replaced the tiny old metal fitting that had a screen with a mushroom thruhull (link below), didn’t put any screen and so far haven’t seen any bug issues, I also upsized the vent line with a proper marine hose; now there’s no odor and I flush the vent line with fresh water after every pump out.

https://defender.com/en_us/forespar-253-series-marelon-mushroom-head-thru-hull-fitting

[peghall]

Why not go with stainless steel painted white? A good hull paint should hold up reasonably well...easily touched up when necessary. There may even paints specifically for metal.


--Peggie

[mottseng]

Originally Posted by sailingharry

Yes, it seems her recommendation is a standard mushroom thru-hull. My hoses are 3/4" and they make a variety of white "plastic" 90 degree versions for $10 or so. If you trust "plastic." While my vents are within an inch or so of the toe rail, they are just a bit forward of amidships. We really hate to bury the rail -- but it does happen. The small vents minimize the inflow. Perhaps a large vent will encourage me to make it happen less often (the admiral would like that!).

LOL... I too avoid having the rail under water!!!