Holding tank vent smell and aeration

[Sleeping Bear]

I clean my tank with massive dose of bleach (4 gal bleach in 30 gal tank), but my tank is plastic metal tanks may not like this.

I fill tank 3/4, add bleach, fill tank to top, let sit and pump out.

The reason I do this is I have a light behind the tank to see where the level is, and it doesn't work well if the sides are covered with poop.

But I digress, and go back to my other post about carbon filters. I really don't care what the inside of the tank smells like, it is the outside that counts.

 

[boomerang]

I clean my tank with massive dose of bleach (4 gal bleach in 30 gal tank), but my tank is plastic metal tanks may not like this.

I fill tank 3/4, add bleach, fill tank to top, let sit and pump out.

The reason I do this is I have a light behind the tank to see where the level is, and it doesn't work well if the sides are covered with poop.

But I digress, and go back to my other post about carbon filters. I really don't care what the inside of the tank smells like, it is the outside that counts.

I think I just heard Peggy scream.

 

[AlanT]

I use a carbon filter on the vent tube. It is a granulated carbon water filter with the standard water filter housing upside down and tilted so if there is ever a disaster it can drain back. The filter costs about ten bucks and lasts about two months constant use.

It has to be a granulated filter because the carbon block filters cause some back pressure, ask me how I know!!

I also added a carbon filter on the vent on a prior boat which had a seawater flush. It completely solved the problem. I built it from Schedule 40 pipe and used carbon granules from a pet shop (it is used in fish tanks).
~A

 

[NightCrawler]

Did you PM Peggie? She might have something else to try.

Peggy knows her stuff. Been on the phone with her a couple of times. We struggled for a long time and ended up with the NoFlex solution. You have to keep on top of it, but odors never returned. Excellent product.

 

[HeadMistress]

I think I just heard Peggy scream.

<LOL> It was a groan actually.

Waste is full of body fats, which creates the scum on the tank walls. Bleach won't dissolve oil or fats, it just removes the color. But detergent will, so next time try a massive dose of Dawn Ultra and let that soak awhile. Better yet, figure out a way to agitate it a bit.

As for vent filters...they actually help to promote the problem they're sold to cure. And like most things, prevention is easier and usually cheaper than cure...and OXYGEN will prevent odors from occurring in holding tanks because odor can only be created in an ANAEROBIC environment. Creating an AEROBIC environment in the tank prevents odor from being generated. A larger diameter, shorter, straighter vent lines is often the solution because it allows better air exchange with the gasses in the tank, but if that's not possible, aeration is the answer. There are many people who've successfully created DIY aerators that work with a fish tank aerator and some perforated hose.

--Peggie

 

[CaptTom]

I'm confused about NoFlex, OxyClean and Sodium Percarbonate.

First off, is SP really one of main ingredients in NoFlex?

From what I've read, SP breaks down into, among other things, Hydrogen Peroxide when it's dissolved in water.

I always thought of OxyClean and Hydrogen Peroxide as bleaching agents. I also connect bleaching with killing bacteria - both aerobic and anaerobic. And it's bad to kill all the bacteria in a holding tank, right? But then how does NoFlex work?

Obviously I'm missing some key facts here.

 

[rslifkin]

In a high enough concentration I'd expect SP to kill bacteria of all types. But in smaller quantities I don't think it's enough to kill aerobic bacteria, but the SP breaking down does release oxygen.

 

[Bacchus]

SPC is a non-clorine bleach. It forms hydrogen peroxide in water which breaks down and produces oxygen which is the key to promoting an aerobic environment and aerobic breakdown of waste that avoids the stink of anaerobic breakdown.
Yes... SPC is listed as the major ingredient (I forget the range but something like 85-95%) note that the mfg does not call it SPC but it's another chemical description that means the same thing.

 

[catalinajack]

SPC is a non-clorine bleach. It forms hydrogen peroxide in water which breaks down and produces oxygen which is the key to promoting an aerobic environment and aerobic breakdown of waste that avoids the stink of anaerobic breakdown.
Yes... SPC is listed as the major ingredient (I forget the range but something like 85-95%) note that the mfg does not call it SPC but it's another chemical description that means the same thing.

And SPC is a whole lot cheaper, and it works a charm.

 

[Brisyboy]

Well, for that pesky smelly tank, I know NoFlex is the go to solution - I used it after discussions (forum and phone) with Peggy and there was no question is solved the problem virtually instantly.

My problem was I kept forgetting to add dose - back came the stinkies. So............plan B I already had one vent line running straight and slightly up hill from the tank. It was about 30mm inside dia so should have helped. Plan B involved running a second vent, same size, from the other side of the tank (also from the top) along side the existing. HOWEVER, on the outside of the hull I installed a small scoop (forgot the name but they are available from chandleries) - horizontally over one of the vent outlets, facing aft. The idea being that the breeze flowing over this creates a venturi effect and sucks air out of the tank, to be replaced by clean (oxygenated) air. I agree the suction must be only very small BUT it has done the job and no smell. BTW, my outlets are side by side so I used the aft one for the venturi. If they were stacked - either one PLUS one either side of the hull would have been just as good, but I had no access.

Thats how I keep plenty of oxygen in the tank.

 

[Comodave]

My tank had the usual 5/8” vent with the filter in it. So that means no air flow through that vent at all. The filter was put in at the factory in a totally inaccessible location. I can see it but no way to even touch it much less change it. So the filter was put in in 1998. Never been changed because you can’t get to it. I added 2 1.5” vents, one to each side of the boat. So there is pretty good air flow through the tank no matter which way the wind is blowing.

 

[Brisyboy]

My tank had the usual 5/8” vent with the filter in it. So that means no air flow through that vent at all. The filter was put in at the factory in a totally inaccessible location. I can see it but no way to even touch it much less change it. So the filter was put in in 1998. Never been changed because you can’t get to it. I added 2 1.5” vents, one to each side of the boat. So there is pretty good air flow through the tank no matter which way the wind is blowing.

Yup, either side is a good solution AND it saves the cost of a scoop

 

[Andy G]

I am about to install a new 160 litre 'plastic' holding tank behing the generator in the ER. I am keen to get it done properly, especially after reading the various posts concerning venting etc.

It seems to me that carbon filters may not be the way to go, but getting adequate amounts of fresh air into the tank is a major plus. I like the idea that George from Brisboy & Comodave have come up with, that is two breather pipes from the top of the tank.

As I am starting completly from scratch I am open to any advice or tips from those who gone gone before.

Cheers & Happy Christmas to all.

Andy

 

[AlanT]

I am about to install a new 160 litre 'plastic' holding tank behing the generator in the ER. I am keen to get it done properly, especially after reading the various posts concerning venting etc.

It seems to me that carbon filters may not be the way to go, but getting adequate amounts of fresh air into the tank is a major plus. I like the idea that George from Brisboy & Comodave have come up with, that is two breather pipes from the top of the tank.

As I am starting completly from scratch I am open to any advice or tips from those who gone gone before.

Cheers & Happy Christmas to all.

Andy

My last boat had a perennially smelly holding tank. Marina neighbors cringed when we flushed. I changed both heads to Marine Elegance and changed supply from saltwater to fresh, changed all hoses and installed a home made carbon filter. Never had another smell to worry about. Never needed any chemicals or additives.

 

[Rated Aargh]

previous owner of my boat installed a simple little aquarium airpump into the top of the tank. he said if the tank starts to smell any just plug that little bugger in for an hour or two and then unplug it (120v). Sure as Sh*t it must apply just enough positive pressure to vent out the tank and the odor goes away.
Just a low budget correction, may not be a final fix type solution but i guess neither is anything else that you have to continually add after each pump out..

 

[Comodave]

previous owner of my boat installed a simple little aquarium airpump into the top of the tank. he said if the tank starts to smell any just plug that little bugger in for an hour or two and then unplug it (120v). Sure as Sh*t it must apply just enough positive pressure to vent out the tank and the odor goes away.
Just a low budget correction, may not be a final fix type solution but i guess neither is anything else that you have to continually add after each pump out..

Same principle as the Groco SweetTank. But it is 12 volts and recommended to run it 24x7. If the poop has enough oxygen it won’t stink. When there is a shortage of oxygen then you get the stinky bacteria.

 

[Invincible Summer]

I appreciate the information on this site. I'm experiencing holding tank odor. I bought Peggy's book on Amazon. By the way, the book is excellent and a must-have for others who read this and also have issues. I have identified several issues (permeated hoses, vent-hose too long, vent filter, etc). I'm fixing those issues, but I do have a question about the Groco Sweet Tank system. I get what the system does, but I wonder what happens when poo is sent from the toilet to the tank. I would assume that it would take a while for bacteria to do it's job. In the meantime, wouldn't a Groco Sweet Tank system force any smell out of the tank and through the vent hose? Maybe y'alls poo doesn't stink ... but I am not that lucky!

 

[lwarden]

Doesn't seem to be a big difference what gets flushed down the toilet when running an aerator. It does help to periodically clean out the holding tank a couple times a year. I'm just flushing down a small scoop of bulk sodium perchlorate every so often and this seems to really help. BTW, I've also found that stuff works well to keep the shower/sink and sump clean, just mix it with hot water and pour it down.

 

[HeadMistress]

When organic matter break down in ANAEROBIC (without oxygen) conditions, it generates hydrogen sulfide and sulfur dioxide (stinky) gasses and methane, which is odorless, but flammable. When it breaks down in AEROBIC (oxygenated) conditions, it convert to CO2, which is odorlesss. Vent filters impede the exchange of air with gasses in the tank, causing the contents to become anaerobic...so instead of preventing odor from being created, a vent filter actually helps to create the problem it's installed to solve.

Aeration, otoh, oxygenates tank contents creating the aerobic condition necessary to prevent odor from occurring, eliminating the need for a filter.

"Vent" thru-hulls are actually designed to keep sea water out of fuel and water tanks. Boat builders use them on holding tank vents because they neither know nor care that holding tanks need to breathe, and using the same thru-hull costs them less than using a different thru-hull on the holding tank vent. Replacing "vent" thru-hulls with open bulkhead (aka "mushroom") fittings has two benefits: they allow the tank to breathe plus allow you to put a hose nozzle against them to back flush the vent line regularly, preventing vent blockages....anything that's trying to set up housekeeping in the vent line gets washed into the tank.

--Peggie

 

[HeadMistress]

I do have a question about the Groco Sweet Tank system. I get what the system does, but I wonder what happens when poo is sent from the toilet to the tank. I would assume that it would take a while for bacteria to do it's job. In the meantime, wouldn't a Groco Sweet Tank system force any smell out of the tank and through the vent hose? Maybe y'alls poo doesn't stink ... but I am not that lucky!

Solid waste is 75% water, so it dissolves very quickly in the tank with or without any added bacteria. Whether the contents of the tank stink or not depends on whether the environment in the tank is aerobic or anaerobic. Aeration creates an aerobic environment.. but not instantly the first time it's turned on. It takes a while--can be several hours--for it to turn the anaerobic conditions that allow odor be generated into aerobic conditions...which is the reason why aerators must run 24-7 whether you're on the boat or not...turning it off allows the environment to become anerobic again.

So yes...when any aeration system is turned on the first time, or after it's been turned off for more than a few minutes, it will push stinky gasses out the vent until it's had time to convert the tank condition to aerobic.

--Peggie

 

[Bacchus]

I build and run a DIY aeration system and never noticed any odor from the vent. I also use and recommend generic SPC / NoFlex.
If interested my aeration system is detailed on my linked Bacchus website in Projects section. Same pump has been running for 10 yrs and total cost was <$50

 

[rslifkin]

For the problem I originally described in this thread, my theory is that I just need more air than I'm pumping into the tank, as it seems like the times when I get some smell are when the tank hasn't been pumped for a few weeks, or when we've been in rough seas and it's been stirred up well. I've been using the Camco TST Max liquid in it this year and as long as I add more every 5 - 7 days, there are no noticeable smell problems. Without it, I still get some smell at times, but nothing like the awful anaerobic stench we got when flushing before I added the aerator.

 

[Flatswing]

I installed the Groco system. I do notice a slight smell when I flush solid waste. It is much improved over before I installed it. A thorough (and I do mean thorough) tank cleaning when and after you install it, helps a lot to get rid of the decades of accumulation which harbor the anaerobic/stinky stuff. You need to run it 24/7 but the current draw is negligible as you can see in the specs. The biggest challenge is mounting the pump so that its vibrations aren't amplified by the hull/bulkhead. Otherwise, a simple install depending on tank access.

 

[dhays]

Thanks to the example of Bacchus, I created a holding tank aerator 3 years ago. Mine is a freshwater flush with a 50 gallon holding tank. It eliminated the holding tank odor. The only other change I made was to replace the typical vent outboard hull fitting with a straight through mushroom (as recommended by Peggie).

It works great and has eliminated all odors. I have run it 24/7 for a couple years but the last year I tend to run it only when we are on the boat or is the tank is reasonably full. If it has sat for a while, I will get a little odor when starting it, but that only last maybe 15-20 minutes.

I use a small amount of NoFlex or Sodium Percarbonate daily when the the boat is being used. I used to use K.O. in my sailboat which had a raw water flush. However, I don't on my current boat with a fresh water flush.

I agree with Bacchus that I don't think that the number and position of holes in the down tube of the bubbler probably make any difference.

Thread with pictures below.

DIY Holding Tank aerator

 

[SteveK]

I see many using fish tank aeration. Does it have to be that way. I cannot find a way to install such an aeration without ripping apart the boat as there is no easy access to tank top except a blind arm. I can either see the fitting or get one hand there.

 

[Comodave]

I see many using fish tank aeration. Does it have to be that way. I cannot find a way to install such an aeration without ripping apart the boat as there is no easy access to tank top except a blind arm. I can either see the fitting or get one hand there.

Can you put an access plate over the tank? Tight access in the engine room is why I didn’t buy a 4788. Bayliner had a winning design with them except the ER was way too tight, for me at least.

 

[SteveK]

Can you put an access plate over the tank? Tight access in the engine room is why I didn’t buy a 4788. Bayliner had a winning design with them except the ER was way too tight, for me at least.

No, the tank is under guest bath cabinet molded counter and extends towards aft. I can remove the ice maker a one foot wide cabinet then lets me see the top of tank fittings offset from base of cabinet.

 

[HeadMistress]

Peggie
I have to disagree... whilevKi have never noticed or looked for condensate in the vent fitting the Bubbling process... small size bubbles vs just air on the surface lends itself to higher dew points. With bubbles the surface area / volume ratio of air is large and has to enhance evaporation and increase the dew point.
If the air is saturated a small temp change results in condensation. Still should not cause any smell.

Point taken.

--Peggie

 

[dhays]

I see many using fish tank aeration. Does it have to be that way. I cannot find a way to install such an aeration without ripping apart the boat as there is no easy access to tank top except a blind arm. I can either see the fitting or get one hand there.

You don't have to access the top of the tank. If you can access the side of the tank, you could likely cut a hole in the tank and install aerator that way.

 

[Comodave]

No, the tank is under guest bath cabinet molded counter and extends towards aft. I can remove the ice maker a one foot wide cabinet then lets me see the top of tank fittings offset from base of cabinet.

Time to get a new boat…