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 can’t 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 ?).

- 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) I’m at a loss of what to do next.

Suggestion are welcome, thanks

Rob

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

Are you sure that salt water with all its biologics isn't the problem?

bayview said:

Are you sure that salt water with all its biologics isn't the problem?

Click to expand...

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.

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

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.

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

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.


--Peggie

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 won’t last long and I will have to find some plastic tube to replace it.

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]

Pete Meisinger said:

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

Click to expand...

so you don't care about sludge just smells with just having the blower

Sea Q said:

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

Click to expand...

[/QUOTE]

Ok that makes sense to me, I have had the vent blocked in the past due to heavy seas ans sloshing of «*poo*» 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

Pete Meisinger said:

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

Click to expand...

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.

Pete Meisinger said:

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.

Click to expand...

I guess you don't understand the principle of promoting aerobic versus anaerobic bacteria in the tank.

It's science. Not venting.

Ok that makes sense to me, I have had the vent blocked in the past due to heavy seas ans sloshing of «*poo*» 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.

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

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 $.

Do you put the hose directly into the Uniseal ?

FlyWright said:

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 $.

Click to expand...

I have been using noflex for over a year now...

HeadMistress said:

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

Click to expand...

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 don’t 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

Bacchus said:

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.

Click to expand...

I have basically the same boat sans bridge...
It is relatively easy to abandon the old vent and install a larger running it forward to the bow area by going under the bed. Mine was out of the water but not essential if you work from a dingy to install the thru hull. Pull the headboard and you have access to that area.

Bacchus said:

I have basically the same boat sans bridge...
It is relatively easy to abandon the old vent and install a larger running it forward to the bow area by going under the bed. Mine was out of the water but not essential if you work from a dingy to install the thru hull. Pull the headboard and you have access to that area.

Click to expand...

Yes that is the plan eventually, I’m just curious about your exact location. I don’t have AC plumbed and the anchor drain area seems too low on the hull. I’m worried that during rough weather water will be forced into the vent line and fill up the tank. One option might be to have the vent hose angle up from the through hull so any water that gets pushed in would only go up a short distance then drain back out. My anchor drain gets water coverage during moderate sea states so a 1-1.5” hole would need to be somewhat protected I would think???

Rob

Diverrob said:

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 don’t want a project this close to departure.

Click to expand...

Any dip in the vent line invites a point where water can collect. This will effectively do the same thing as the trap under a sink. It'll block any air from passing. We had this problem in our EB47. The vent line wasn't supported well enough and there was 'just enough' dip to allow water to collect and a trap to form. Using some hose straps eliminated the dip.

The next step was to use both NoFlex AND their toilet bowl cleaner. Nothing else. No other chemicals. When we leave the boat for the week we'll add the NoFlex, clean the bowls and then flush a few times to make sure there's nothing left in the lines.

The combination of the vent, NoFlex and bowl cleaner has solved our tank smells.

https://www.amazon.com/gp/product/B07C7HRV4P
https://www.amazon.com/gp/product/B07DFBLKNG

Pura Vida said:

Do you put the hose directly into the Uniseal ?

Click to expand...

No...you insert a short piece of pvc pipe (it shouldn't extend more than an inch inside the tank) that has a 1" OUTER diameter (to fit into a 1" hose) and put the vent line on it, secured by hose clamps same as you'd put it onto any other hose fitting. The pipe can be a 90 or 45 (available from the plumbing dept of any big box hardware store) if necessary.


--Peggie

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

You'll have to replace the vent thru-hull with a 1" bulkhead fitting anyway, so it's the best time to find a better location for it.


And btw...you can prevent future vent blockages by backflushing the vent line every time you wash the boat and/or pump out.


--Peggie

Another method to get more air into the waste tank....remove the pump out cap and leave open for a few hours. We do this initial when we get to the boat. A few hours works perfect.

jimdavi said:

Another method to get more air into the waste tank....remove the pump out cap and leave open for a few hours. We do this initial when we get to the boat. A few hours works perfect.

Click to expand...

I don't know why so many people think that opening the deck pumpout cap introduces any air into the tank, because the pumpout line runs from the bottom of the tank to the deck pumpout fitting. So there's no way that opening the deck pumpout cap can introduce air into the tank above the surface of the contents to "ventilate" the tank. Relieving any pressure created by a partial vent blockage is the only thing it can accomplish...and if you back flush the vent line every time you pump out and/or wash the boat, you won't ever have a blocked vent.

If your vent thru-hull isn't one that makes back flushing possible, replace the "vent" thru-hull with one that does--an open "bulkhead" fitting that you put a hose nozzle against. If there's a filter in the vent line, it'll have come out 'cuz filters can't get wet. But filters actually help to create the problem they're sold to solve so you're better off without it anyway.

--Peggie

HeadMistress said:

I don't know why so many people think that opening the deck pumpout cap introduces any air into the tank, because the pumpout line runs from the bottom of the tank to the deck pumpout fitting. So there's no way that opening the deck pumpout cap can introduce air into the tank above the surface of the contents to "ventilate" the tank. Relieving any pressure created by a partial vent blockage is the only thing it can accomplish...and if you back flush the vent line every time you pump out and/or wash the boat, you won't ever have a blocked vent.

If your vent thru-hull isn't one that makes back flushing possible, replace the "vent" thru-hull with one that does--an open "bulkhead" fitting that you put a hose nozzle against. If there's a filter in the vent line, it'll have come out 'cuz filters can't get wet. But filters actually help to create the problem they're sold to solve so you're better off without it anyway.

--Peggie

Click to expand...

Clearly, I’m no expert...what is the difference if the bottom of the holding tank is exposed to air rather than the top? Do the microorganisms only live on the top of the waste product?

jimdavi said:

Clearly, I’m no expert...what is the difference if the bottom of the holding tank is exposed to air rather than the top? Do the microorganisms only live on the top of the waste product?

Click to expand...

The issue is that you're only exposing a very small amount of waste to air. In the case of my tank, it would be just the top surface of the waste in the 1.5 inch diameter dip tube for pumpout.

jimdavi said:

Clearly, I’m no expert...what is the difference if the bottom of the holding tank is exposed to air rather than the top? Do the microorganisms only live on the top of the waste product?

Click to expand...

Opening at the deck allows sewage to flow up the pipe to the level inside the tank. So you now have what a 2 inch circle exposed to air? Air is not going to go past that fluid and into the top of the tank where there is more air and more surface of sewage to interact with.