Holding Tank Vent Filter

Before we left on this cruise I replaced my filter with a Dometic filter, see pic below

I noticed after that, on a flush, air was bubbling out the through hull for the macerator once the through hull was left open after leaving the States. Air only as there is a big loop in the hose prior to discharge.

So clearly the tank was venting through the macerator and not the vent. I checked the filter and owners manual to make sure that it didn't have arrows on it showing a one way flow so I might have put it on backwards - it does not seem to matter which way it goes on.

We are off shore tomorrow so I will pump out the holding tank and get rid of all the pressure. Then I am going to remove the filter and put my small compressor on the hose from the filter to the hull vent to make sure that is not blocked.

Questions: those with this filter, can you confirm that it does not matter which way it goes on?

Secondly, any other thoughts as to the issue?

Greetings,
Mr. m. I'm in the "don't want or need a filter" crowd. Yes, there are arguments pro and con but IMO a properly functioning and vented holding tank does not need a filter.

RT Firefly said:

Greetings,
Mr. m. I'm in the "don't want or need a filter" crowd. Yes, there are arguments pro and con but IMO a properly functioning and vented holding tank does not need a filter.

Click to expand...

That's one of my options, take the filter off and join up the two hoses. I need to make sure the vent line to hull side is clear first though, otherwise that won't solve anything.

Is it possible it had "caps" that needed to be removed first?

Just looked at the manual and it states:

"Remove the red stoppers from both connectors of the vent filter."

Is it possible one or both of these was accidentally left in place? This would certainly cause the problem you're seeing.

Ken

I don’t like filters in the vent. Just get air into the tank and the smells will go away.

kchace said:

Is it possible it had "caps" that needed to be removed first?

Just looked at the manual and it states:

"Remove the red stoppers from both connectors of the vent filter."

Is it possible one or both of these was accidentally left in place? This would certainly cause the problem you're seeing.

Ken

Click to expand...

Yes, there were two red caps, both definitely removed. Also I don't think it would have gone onto the hose threads otherwise.

I'd look at the vent hose for a kink in the vent hose, usually about the turn of the bilge. Old hose curves can turn into hose corners.
Look for low spots that may be holding a water trap.
Also if the filter gets "moisture" into the charcoal it will become ineffective and decrease venting capacity.
If there is a direction for the vent, logic dictates the D in Dometic to the holding tank side.
But logic and boats don't always travel side by side.

Just looked at the photo, "Eco" to tank side.

Greetings,
Welcome aboard Mr./Ms. SL.

Comodave said:

I don’t like filters in the vent. Just get air into the tank and the smells will go away.

Click to expand...

If you can't get enough air in via vent by increasing size, adding a second vent, straightening it out, etc - all recommendations by Peggie
Adding air via a bubbler will accomplish the same thing - I used an inexpensive 12V fish tank aerator that has worked well for 3 seasons.

Anaerobic bacteria - BAD - SMELL is VERY BAD
Aerobic bacteria - GOOD - No More BAD SMELL

Get rid of the vent filter. They actually help to create the very problem they're sold to solve! But first check the vent thru-hull for a blockage...it's the most common location for one. Dirt daubers love to build their nests in and spring is time of year that they do it. If the thru-hull is one that makes that impossible, use a screwdriver blade, ice pick or whatever works to dig out whatever may be blocking it. Knock out any screen...screens get clogged up with dust, pollen and corrosion.


--Peggie

menzies said:

Before we left on this cruise I replaced my filter with a Dometic filter, see pic below

I noticed after that, on a flush, air was bubbling out the through hull for the macerator once the through hull was left open after leaving the States. Air only as there is a big loop in the hose prior to discharge.

So clearly the tank was venting through the macerator and not the vent. I checked the filter and owners manual to make sure that it didn't have arrows on it showing a one way flow so I might have put it on backwards - it does not seem to matter which way it goes on.

We are off shore tomorrow so I will pump out the holding tank and get rid of all the pressure. Then I am going to remove the filter and put my small compressor on the hose from the filter to the hull vent to make sure that is not blocked.

Questions: those with this filter, can you confirm that it does not matter which way it goes on?

Secondly, any other thoughts as to the issue?

Click to expand...

I'm with Peggy - a no filter fan. Although most folks concentrate on the thru hull as a source of blockage, in my case, the 90 deg vent fitting on the tank was totally occluded. If the tank has ever been really full, especially in a sea, definite chance for solids to gum up the tank fitting. After I cleaned the tank fitting & replaced the filter with new tubing, smell is gone & pump outs are much easier..

"Adding air via a bubbler will accomplish the same thing - I used an inexpensive 12V fish tank aerator that has worked well for 3 seasons."

This is the solution the big charter tubs use ($10,000+ a day) while Med moored .

No filter on mine. I replaced the vent line, tank connection, and through hull vent with larger diameter parts. After each pump out, with a dock hose, I flush a little water into the vent to make sure the line is clear. Works great and no odor.

Ted

Although most folks concentrate on the thru hull as a source of blockage, in my case, the 90 deg vent fitting on the tank was totally occluded. If the tank has ever been really full, especially in a sea, definite chance for solids to gum up the tank fitting.

I neglected to mention this because although heeling makes it common for waste to spill into the vent on sailboats, its relatively rare on powerboats. Which is not say it can't happen...your experience makes it obvious that it can. Which is another good reason to replace the "vent" thru-hull with an open bulkhead thru-hull even if you don't "upgrade" to a larger diameter vent line: You can stick a hose nozzle up against it to back flush the vent line every time you pump out and/or wash the boat.



--Peggie

Years ago on advice from Peggy we put in Groco Sweetank because of the horrible smell coming out of the vent when we flushed a head. After 2 hours of running the air pump the smell was gone and never came back for the 8 more years we owned the boat. We never again put any chemicals in the head just used the air system.

If you fill up your holding tank and it overflows into the Vent line, it will block up the filter. Time for yet another new vent line filter.
Not sure if that happened.....

Instead of replacing the filter, why not replace the vent thru-hull with an open thru-hull that provides better air exchange, start using No-Flex Digestor Noflex Digestor in the tank and just get rid of the filter?


--Peggie

HeadMistress said:

Instead of replacing the filter, why not replace the vent thru-hull with an open thru-hull that provides better air exchange, start using No-Flex Digestor Noflex Digestor in the tank and just get rid of the filter?


--Peggie

Click to expand...

+1

Taras said:

If you fill up your holding tank and it overflows into the Vent line.....

Click to expand...

And btw...If you don't have a tank level indicator, or have one that's quit working, I suggest you check out the SCAD monitor Scad Tank Monitors The sender goes on the outside of the tank, so it can never become clogged with the animal fats in waste requiring removal to clean. Provides an accurate empty, 1/4, 1/2, 3/4 and FULL reading, and if your current system is a SeaLand TankWatch, itcan use the same wiring.



--Peggie

HeadMistress said:

Instead of replacing the filter, why not replace the vent thru-hull with an open thru-hull that provides better air exchange, start using No-Flex Digestor Noflex Digestor in the tank and just get rid of the filter?


--Peggie

Click to expand...

+2

Just upgraded to 1" vent too

HeadMistress said:

And btw...If you don't have a tank level indicator, or have one that's quit working, I suggest you check out the SCAD monitor Scad Tank Monitors The sender goes on the outside of the tank, so it can never become clogged with the animal fats in waste requiring removal to clean. Provides an accurate empty, 1/4, 1/2, 3/4 and FULL reading, and if your current system is a SeaLand TankWatch, itcan use the same wiring.

Click to expand...

I completely agree and have been doing this with a SCAD for about 10 years.

FWIW, I followed the experience of others here and added a 12v bait tank aerator to my holding tank. It immediately took care of any holding tank odors. I’ve only had it connected now for about 6 months. The real question will be how long the pump lasts. They are pretty cheap so if it fails after a few years I’m not too concerned as it would be easy not replace. I have it wired to my shower sump pump circuit . I didn’t leave it running during the winter when the boat didn’t get used as much, but when I turn it on after sitting a while, it only takes about 15 minutes for any head smell to be gone at the hull vent.

Took the filter off and now have vent line only.

In trying to understand how they plumbed this system. I see this valve.

There is a vent line connected to the top of the loop in the hose from the macerator pump to the through hull. This then loops back to join the main vent line in a T above the holding tank. This valve is on that secondary vent line.

Anyone know what it is and it's function?

Wondering if it a pressure valve that opens if the main vent line gets clogged to prevent pressure in the system?

It's not uncommon--although a bad idea--to install a vent line on the top of a vented loop to solve the problem of waste squirting out the hole in the nipple at the top of the loop. Apparently someone told him that what he really needed was an air valve. Without a clue as to what an air valve in a vented loop is, he installed that valve. Remove both and replace the vent line coming off the top of the loop with the air valve that designed to go there...it's a small piece that threads into the nipple on the top of the loop. Photos show what a vented loop with air valve should look like. There appears to be one in the loop on the black hose...unless it's just capped off...which, considering how the holding tank vent is plumbed, is possible.

Why is it a bad idea to put a vent line on the loop instead? Because it doesn't prevent squirting, it just traps it. In a very short time waste, salt and sea water mineral buildup clogs the line, turning a vented loop into an UNvented loop that no longer has any ability to prevent a siphon.

To clarify, this is not on the main vent line to the hull side, but a second vent line from the below waterline discharge hose back to a T with the main vent hose above the holding tank.

HeadMistress said:

Instead of replacing the filter, why not replace the vent thru-hull with an open thru-hull that provides better air exchange, start using No-Flex Digestor Noflex Digestor in the tank and just get rid of the filter?


--Peggie

Click to expand...

Menzies,
Sorry for the one question thread drift, but since Peggy is posting on this thread Good luck getting this system working well.

Peggy,
You used to recommend using KO in the holding tank. Have you changed your opinion and now prefer Noflex?
Thanks,
Tom

HeadMistress said:

Why is it a bad idea to put a vent line on the loop instead? Because it doesn't prevent squirting, it just traps it. In a very short time waste, salt and sea water mineral buildup clogs the line, turning a vented loop into an UNvented loop that no longer has any ability to prevent a siphon.

Click to expand...

This is another of those cases that when I read your explanation it makes so much sense that I fool myself into thinking it would have been self-evident to me. However, I know it wouldn't have been. Once again, thanks for your contributions. I always learn stuff.

You used to recommend using KO in the holding tank. Have you changed your opinion and now prefer Noflex?

K.O. was the first bio-active holding tank treatment..till we introduced in 1987, the only tank products were toxic chemicals and a couple of wimpy enzyme products. It took me a while to find out why it worked perfectly in about 90% of tanks but didn't work worth a damn--and in some cases made the odor even worse--in the remaining 10%: the tank vent has to supply enough air exchange to create and keep the environment in the tank aerobic. And that's still true: K.O. can't prevent odor in anaerobic conditions. But like most things, bio-chemistry has evolved in 30 years and there are now products--notably No-Flex--that need a LOT less oxygen to do the job. And as much "parental pride" as I have in K.O., I have to recommend No-Flex until/unless I know the system is sufficiently ventilated to allow K.O. to work.


--Peggie

menzies said:

To clarify, this is not on the main vent line to the hull side, but a second vent line from the below waterline discharge hose back to a T with the main vent hose above the holding tank.

Click to expand...

I have NO idea why it would be there, nor the purpose of the valve...but I do know for certain that teeing anything--and especially not a line off a holding tank discharge line--into a holding tank vent line is a bad idea. I also have no idea why that valve is where it is or what it accomplishes, if anything.

So I suggest you re-plumb the system without the valve and the line that tees into the vent, and with an air valve in the vented loop if there isn't one. If there is, it prob'ly either needs cleaning or possibly replacement.

And while you're at it, replace the vent thru-hull with one that'll allow some air exchange in and out of the tank--and also allow you to prevent vent blockages by sticking a hose nozzle against it and backflushing the vent line.

--Peggie
I'm seriously considering replacing the Einstein quote in my signature with "nothing can ever be foolproof because fools are so creative!"

Peggy,
Thanks so much for the quick and detailed response. As soon as I run out of KO I will switch to Noflex.
I am also still using CP for cleaning.
I agree with Menzies, always learn something from you.
Thanks again,
Tom