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Old 08-08-2020, 08:31 AM   #1
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Holding tank vent smell

Hey everyone!

I know this is not a new subject and have read many threads on the subject and made a few modifications to try and fix my issue but canít seem to get there. I have a 2007 Mainship Trawler with the original 35G holding tank that has a saltwater flush system. I fully know that the stock vent line is too small and that getting air into the tank is key so here is what I have done and maybe someone can help me out (please be kind &#128526.

- I have installed a bubble system into the tank and run it 24/7
- Pump out and flush the tank with fresh water leaving it 1/2 full of just water after every outing
- Strictly use Xaal Noflex in the tank during use and after flushing
- currently no vent filter

My issue is the bubbler creates a constant flow out of the tank and it smells 😬 so when we have other boats come alongside they get the vent smell. Other than adding a filter (I know this is not recommended) or turning off the bubbler when we have other alongside (defeats the point of getting air into the tank) Iím at a loss of what to do next.

Suggestion are welcome, thanks

Rob
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Old 08-08-2020, 10:09 AM   #2
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An eration, correctly designed, installed, operated and maintained will completely eliminate odor out the vent. There are a couple of possible reasons why yours isn't doing that.


1. It doesn't run 24/7/365. An aerator can't aerate when it's not introducing air into the tank contents, so they become anaerobic, generating stinky gasses, especially if the tank vent is too small and/or has a thru-hull that prevents air exchange. When it's turned on again, the air introduced just pushes stinky gasses out the vent until it can restore aerobic conditions, which can take several hours.


2. You installed a "bubbler" using a single hose in the middle of the tank that only creates a column of air instead one with perforated piping that lies across the bottom of the tank, distributing air throughout the contents. Although that can work in smaller tanks, and might also work in larger ones if the hose is perforated so that air is distributed throughout instead of only at the bottom. But that needs to run 24/7/365 to accomplish much too.


The installation, operation and maintenance instructions for the Groco Sweettank system should be enlightening. Groco Sweetank


--Peggie
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Old 08-08-2020, 10:28 AM   #3
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Are you sure that salt water with all its biologics isn't the problem?
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Old 08-08-2020, 11:58 AM   #4
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Are you sure that salt water with all its biologics isn't the problem?
I was about to say the same thing. My first solution would be to get a fresh water system. That would certainly help I would think.
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Old 08-08-2020, 12:39 PM   #5
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Thanks Peggy 😄

My bubble system does actually run 24/7 365 I have not turned it off since I installed it over a year ago. I did have initially a line that ran across the bottom with many holes to stir up and bubble the tank. Now that system lasted about a year but then plugged and corrosion caused it to fail (although it did not eliminate the smell either). I now have a plastic tube that does not run to the bottom so that seems to be part of the issue. I will adjust the system to use Cooper or plastic tube and run it across the bottom of the tank but that will need to wait until after our trip this summer.

As for switching to a fresh water system that will not be possible as I only hold 70 gallons of fresh water and we will need it for domestic use.

Rob
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Old 08-08-2020, 01:12 PM   #6
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I did basically what you did by installing bubbler and started using NoFlex and it eliminated our odor problem. I did install mine as Peggie suggests with a perforated pipe and bottom of tank by using the macerator outlet. Other difference is we are in fresh water.
I was finally able to abandon our old vent and installed a new larger straighter one under the fwd bed to the bow and installed a straight mushroom thru hull in the area of AC discharge & anchor locker drain.
I do run my bubbler 24/7 during the season.
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Old 08-08-2020, 03:59 PM   #7
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I would NEVER contradict Peggy, but...

Instead of having a bubbler in the tank why not have a small blower adding air to the surface and letting it escape through two vents, one on each side of the boat. I guess I don't see the need to bubble the waste, all you really want to do is add lots of fresh air.

I think the real key to the issue though is probably using salt water to flush. If your holding tank only holds 35 gallons all you would need to do is add about a 25 gallon fresh water tank near the toilet. That should be easy enough to do.

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Old 08-08-2020, 04:51 PM   #8
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Salt water can create intake odor problems and odor from the toilet discharge line, but there's so much bacteria in waste that a tankful of it doesn't even notice whether you're flushing with salt water or fresh. Bacteria can only generate malodorous gasses--sulfur dioxide and hydrogen sulfide-- in anaerobic an environment. When waste breaks down in an aerobic environment, it converts to CO2, which is odorless. BUT--Co2 doesn't rise, so if there isn't enough air exchange, either passively above the tank via tank venting or through aeration, it can build up on the surface of the tank contents and "smother" them, creating the anaerobic conditions needed to generate the stinky gasses. It has NOTHING to do with whether the toilet flushes with sea water or fresh.

If his aerator hasn't worked, swapping out the "vent" thru-hull for an open bulkhead fitting is the first thing I'd try.

Rob said I did have initially a line that ran across the bottom with many holes to stir up and bubble the tank. Now that system lasted about a year but then plugged and corrosion caused it to fail.

Only metal corrodes, plastic doesn't, which is why metal doesn't belong in a tank. And because aeration piping across the bottom will become clogged with sludge, it requires maintenance that you apparently didn't do--thoroughly flushing out the tank to get rid of the sludge and sometimes even removing the hose to clean it out if it's packed. So it's not surprising that it didn't eliminate the odor...no air was going through the piping.

That it didn't work very well before it clogged up either confirms my suspicion that the "vent" thru-hull (designed to keep sea water out of fuel and water tanks, but boat builders use 'em on all tanks 'cuz it costs 'em less to buy one type in bulk than to buy the right kind for waste vents) isn't allowing enough air exchange for the aerator to force the CO2 out of it.


So before doing anything else, try replacing the vent thru-hull and adding No-Flex to the tank...it often works in tanks that aren't aerobic enough for the vent to do it on its own.


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Old 08-08-2020, 05:33 PM   #9
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I put a Groco Sweettank system in a previous boat on Peggies recommendations and the smell from the 80 gallon holding tank was gone in 2 hours. I never added any chemicals after the install and we never had any odor out the vent for the next 8 years we owned the boat. We just put a Sweettank in our current boat. Groco in their wisdom went from a fiberglass dip tube to a metal one so I suspect that it wonít last long and I will have to find some plastic tube to replace it.
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Old 08-08-2020, 07:43 PM   #10
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Hi Rob
if the bubbler and the Noflex don't fix it it might be something else

People over look the vent line from the tank
If waste get in it the Noflex or the bubbler will not help getting rid of the smell because there is no contact with the waste there .

Try back flushing the vent line back into the tank with a garden hose.
Don't be to hard with this because you don't want to pressurize your tank.
Don't know why but boat people down under have a big problem with this (maybe they have rougher seas and it sloshes into the line )
They install a flush line to blow the vent from the tank ; over the side to the vent . They are all surprised what comes out .
One guy said it was like a elephant letting go full blast across the dock .

What is the size, age and condition of your holding tank and how long have you been using Noflex .
Dave




Suggestion are welcome, thanks

Rob[/QUOTE]
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Old 08-08-2020, 07:58 PM   #11
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Quote:
Originally Posted by Pete Meisinger View Post
I would NEVER contradict Peggy, but...

Instead of having a bubbler in the tank why not have a small blower adding air to the surface and letting it escape through two vents, one on each side of the boat. I guess I don't see the need to bubble the waste, all you really want to do is add lots of fresh air.

I think the real key to the issue though is probably using salt water to flush. If your holding tank only holds 35 gallons all you would need to do is add about a 25 gallon fresh water tank near the toilet. That should be easy enough to do.

pete
so you don't care about sludge just smells with just having the blower
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Old 08-09-2020, 12:57 AM   #12
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Hi Rob
if the bubbler and the Noflex don't fix it it might be something else

People over look the vent line from the tank
If waste get in it the Noflex or the bubbler will not help getting rid of the smell because there is no contact with the waste there .

Try back flushing the vent line back into the tank with a garden hose.
Don't be to hard with this because you don't want to pressurize your tank.
Don't know why but boat people down under have a big problem with this (maybe they have rougher seas and it sloshes into the line )
They install a flush line to blow the vent from the tank ; over the side to the vent . They are all surprised what comes out .
One guy said it was like a elephant letting go full blast across the dock .

What is the size, age and condition of your holding tank and how long have you been using Noflex .
Dave




Suggestion are welcome, thanks

Rob
[/QUOTE]

Ok that makes sense to me, I have had the vent blocked in the past due to heavy seas ans sloshing of ę*poo*Ľ so I will try flushing. I have only to this point uses LP air to clear the blockage but not flushed with fresh water. My tank is original so 13 years old now, is 35 gallons and I have been using noflex for over a year now.

Peggy

Thanks for the vent tip, I will investigate that as well. When I first bought the boat the screen in the vent was plugged so I removed it but am still using the original fitting.

Rob
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Old 08-09-2020, 07:23 PM   #13
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Quote:
Originally Posted by Pete Meisinger View Post
I would NEVER contradict Peggy, but...

Instead of having a bubbler in the tank why not have a small blower adding air to the surface and letting it escape through two vents, one on each side of the boat. I guess I don't see the need to bubble the waste, all you really want to do is add lots of fresh air.

I think the real key to the issue though is probably using salt water to flush. If your holding tank only holds 35 gallons all you would need to do is add about a 25 gallon fresh water tank near the toilet. That should be easy enough to do.

pete
Pete
I have this 12V bubbler running 24/7 and draws less than 1/2 A. I dont know if you could find a blower that would run on that power.
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Old 08-09-2020, 07:31 PM   #14
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I would NEVER contradict Peggy, but...

I guess I don't see the need to bubble the waste, all you really want to do is add lots of fresh air.
I guess you don't understand the principle of promoting aerobic versus anaerobic bacteria in the tank.

It's science. Not venting.
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Old 08-09-2020, 08:03 PM   #15
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Ok that makes sense to me, I have had the vent blocked in the past due to heavy seas ans sloshing of ę*poo*Ľ so I will try flushing. I have only to this point uses LP air to clear the blockage but not flushed with fresh water. My tank is original so 13 years old now, is 35 gallons and I have been using noflex for over a year now.

Peggy

Thanks for the vent tip, I will investigate that as well. When I first bought the boat the screen in the vent was plugged so I removed it but am still using the original fitting.

Rob[/QUOTE]

Peggie is a great source of info.
She loves to be helpful and she does know her stuff.
Just remember we are not standing there in your shoes to see all of the things going down .
Her book is a wealth of info .

Advice is just from what we have seen in the past and i'm sure new scenarios evolve will pop up.
Lets just hope problems can be solved so we can all spend Quality time on the water.
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Old 08-09-2020, 08:45 PM   #16
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When I first bought the boat the screen in the vent was plugged so I removed it but am still using the original fitting.
In that case you already have an open thru-hull that you can put a hose against and backflush the vent line. The only other thing that may be preventing your bubbler from eliminating odor out the vent is the path the vent line takes. A path from the tank to the thru-hull that isn't straight impedes the air exchange needed to keep the tank aerobic..so does a filter in the vent line. So, tell me about your vent line.

And btw...how much clearance do you have above the tank? Replacing the 5/8" vent fitting on it with a 1" or even 1.5" is actually very easy if you have enough space above the tank use a power drill to install a li'l gadget called the Uniseal UNISEAL . That would be a huge improvement in the air flow through it.

--Peggie
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Old 08-09-2020, 08:48 PM   #17
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Before you spend another dime, buy and try NoFlex. I'd it works for you as well as it worked for me, your problem will be solved. If not, you haven't spent much chasing the next possible solution.

Sodium percarbonate is an alternative to NoFlex that costs even less $.
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Old 08-09-2020, 08:59 PM   #18
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Do you put the hose directly into the Uniseal ?
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Old 08-09-2020, 09:18 PM   #19
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Before you spend another dime, buy and try NoFlex. I'd it works for you as well as it worked for me, your problem will be solved. If not, you haven't spent much chasing the next possible solution.

Sodium percarbonate is an alternative to NoFlex that costs even less $.
I have been using noflex for over a year now...
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Old 08-09-2020, 09:28 PM   #20
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When I first bought the boat the screen in the vent was plugged so I removed it but am still using the original fitting.
In that case you already have an open thru-hull that you can put a hose against and backflush the vent line. The only other thing that may be preventing your bubbler from eliminating odor out the vent is the path the vent line takes. A path from the tank to the thru-hull that isn't straight impedes the air exchange needed to keep the tank aerobic..so does a filter in the vent line. So, tell me about your vent line.

And btw...how much clearance do you have above the tank? Replacing the 5/8" vent fitting on it with a 1" or even 1.5" is actually very easy if you have enough space above the tank use a power drill to install a li'l gadget called the Uniseal UNISEAL . That would be a huge improvement in the air flow through it.

--Peggie
Ok so went down to the boat today and pulled the vent line off the tank and a puff of air came out! Obviously there must have been a partial blockage. I flushed the line and blew it out with LP air, now the airflow is unrestricted. The path that the vent line takes is not ideal and too long. It runs along side the tank at no angle which does not promote drainage. And as expected it is tie wrapped every 12*inches which makes removal extremely difficult. I will replace this eventually but we leave on Friday so donít want a project this close to departure.

I have room on top of the tank so will look at this fitting you suggested and increase the vent size and possibly location.

Rob
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