Holding tank vent smell and aeration

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I had the odor problem several years ago. After some thought, I crated a vent filter from pvc tubing using charcoal filter material from an aquarium supply co. lasts quite a while. When the odor starts to build, I just change the charcoal. Bob

The problem with vent filters is that they block air flow into the tank so it promotes anerobic bacteria which is what stinks. If you get good airflow into the tank it promotes aerobic bacteria which doesn’t stink.
 
Something else to consider if your system is a Vacuflush. I'm in the process of rebuilding the vacuum generator on my boat and have the entire thing pulled apart. The stench of the scale buildup on the interior of the pump and fittings was pretty bad before I used acid to strip it down (a lovely job). I would imagine that air moving through that pump and any lines with the dried pee scale is going to create an odor no matter how sweet the tank is. FWIW I have an aerator and for the most part that solved the tank odor, but you still smell a bit during flushing and I'm wondering if this smelly scale is part of the issue.
 
Something else to consider if your system is a Vacuflush. I'm in the process of rebuilding the vacuum generator on my boat and have the entire thing pulled apart. The stench of the scale buildup on the interior of the pump and fittings was pretty bad before I used acid to strip it down (a lovely job). I would imagine that air moving through that pump and any lines with the dried pee scale is going to create an odor no matter how sweet the tank is. FWIW I have an aerator and for the most part that solved the tank odor, but you still smell a bit during flushing and I'm wondering if this smelly scale is part of the issue.

That sounds like it could be a factor. Smells getting pushed from the Vacuflush system to the tank, then getting blown out the vent.

No Vacuflush in my setup though.
 
Something else to consider if your system is a Vacuflush. I'm in the process of rebuilding the vacuum generator on my boat and have the entire thing pulled apart. The stench of the scale buildup on the interior of the pump and fittings was pretty bad before I used acid to strip it down (a lovely job). I would imagine that air moving through that pump and any lines with the dried pee scale is going to create an odor no matter how sweet the tank is. FWIW I have an aerator and for the most part that solved the tank odor, but you still smell a bit during flushing and I'm wondering if this smelly scale is part of the issue.

Now would be the time to convert to a Raritan Marine Elegance head. It may be about as cheap as buying all the parts for the VF head. We ripped out the VF in our boat, and the last 3 boats, and put in a ME head. Absolutely love it.
 
Something else to consider if your system is a Vacuflush. I'm in the process of rebuilding the vacuum generator on my boat and have the entire thing pulled apart. The stench of the scale buildup on the interior of the pump and fittings was pretty bad before I used acid to strip it down (a lovely job). I would imagine that air moving through that pump and any lines with the dried pee scale is going to create an odor no matter how sweet the tank is. FWIW I have an aerator and for the most part that solved the tank odor, but you still smell a bit during flushing and I'm wondering if this smelly scale is part of the issue.
Smell inside when flushing is frequently organic matter sitting in the inlet line and decomposing. If is strongest 1st flush after sitting the probability increases.
If outside its then tank sludge/ vent related.
Sodium percarbonate / NoFlex helps breakdown tank build up over time.
 
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Aren’t VF usually freshwater flush? Mine were.
 
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Aren’t VF usually freshwater flush? Mine were.
Yes but OP has said no VF.
Long threads get confusing with conjecture but no VF and Im ASSUMING raw water flush but no stated so far?
 
Something else to consider if your system is a Vacuflush. I'm in the process of rebuilding the vacuum generator on my boat and have the entire thing pulled apart. The stench of the scale buildup on the interior of the pump and fittings was pretty bad before I used acid to strip it down (a lovely job)

That scale buildup--which are urine crystals called struvites, btw--is a direct result of using too little water to flush and failure to run a full bowl of water through it once a day. Flush water flow is too wimpy to fill the hose...Leaving the pedal down just barely long enough for the suction to empty the bowl doesn't rinse at all. The pedal should stay down at least 3 full seconds after urine only, 7-10 seconds after solids--to which you should have added 1/2 bowl of water before use. Another quart of a water following the flush will rinse out the hose.

I've written a li'l treatise that I call "VacuFlush 101" that explains how it works (an amazing number of owners think they know but actually don't) and how much water it really needs to prevent 90% of problems with it. If you'd like to have a copy, send me a PM that includes your email address (no way to attach anything to a PM).
And fwiw, VF was the toilet on my last two boats and I was a dealer for 10 years...so I'm intimately acquainted with it.


--Peggie
 
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Following with interest.
I have recent Marine Elegance (fresh water flush) heads, new hoses. Because of persistent vent smell (no charcoal filter). I installed a Groco sweet tank 6 weeks ago. At the same time, I cleaned a lot of plaque like material from the bottom of the tank. Instead of losing the smells within 2 hrs as some suggested. I now have a constant smell from the vent. If the BR window is open, now the smell wafts back in if the wind is on the STBD bow. Frustrating.
 
Following with interest.
I have recent Marine Elegance (fresh water flush) heads, new hoses. Because of persistent vent smell (no charcoal filter). I installed a Groco sweet tank 6 weeks ago. At the same time, I cleaned a lot of plaque like material from the bottom of the tank. Instead of losing the smells within 2 hrs as some suggested. I now have a constant smell from the vent. If the BR window is open, now the smell wafts back in if the wind is on the STBD bow. Frustrating.

That sounds like my issue. Wind was light today, so easier to smell things. Still a faint smell from the vent, but nothing terrible. Wind has to be almost dead to notice it and you have to be within a few feet of the vent.

So mine still isn't all there, but it's better than the stench we started with.

I wonder why aeration doesn't seem to be enough for some tanks. Or if it's possibly a case of needing even more air flow.
 
The first boat that we put a Sweetank in had an 80 gallon fiberglass holding tank. Since it was fiberglass I could not see inside it at all so I have not idea if it was dirty or not. But the smell outside was absolutely horrible when we flushed the head. On Peggies advice I put in a Sweetank. Almost exactly 2 hours after I turned it on the smell was gone. I could put my nose within 3” of the vent and smell nothing. We had that boat for another 8 years and I never added any chemicals to the tank and never had anymore smell. I don’t understand why yours isn’t working. We put a Sweetank in another boat and had no problems with it but I sold that boat about a year later. Maybe call Groco for some advice.
 
If you have access you might consider installing a clean put port so you could remove it, inspect and blast any sediment w high pressure hose to ensure a clean tank to start.
 
If you have access you might consider installing a clean put port so you could remove it, inspect and blast any sediment w high pressure hose to ensure a clean tank to start.

I've been thinking about that. Just have to drill a big enough hole into the tank at some point. Access to my tank is good, fortunately.
 
Something else to consider if your system is a Vacuflush. I'm in the process of rebuilding the vacuum generator on my boat and have the entire thing pulled apart. The stench of the scale buildup on the interior of the pump and fittings was pretty bad before I used acid to strip it down (a lovely job)

That scale buildup--which are urine crystals called struvites, btw--is a direct result of using too little water to flush and failure to run a full bowl of water through it once a day. Flush water flow is too wimpy to fill the hose...Leaving the pedal down just barely long enough for the suction to empty the bowl doesn't rinse at all. The pedal should stay down at least 3 full seconds after urine only, 7-10 seconds after solids--to which you should have added 1/2 bowl of water before use. Another quart of a water following the flush will rinse out the hose.

I've written a li'l treatise that I call "VacuFlush 101" that explains how it works (an amazing number of owners think they know but actually don't) and how much water it really needs to prevent 90% of problems with it. If you'd like to have a copy, send me a PM that includes your email address (no way to attach anything to a PM).
And fwiw, VF was the toilet on my last two boats and I was a dealer for 10 years...so I'm intimately acquainted with it.


--Peggie

Apologies for the thread derail rslifkin but wanted to respond to Peggy. I'm sure you are 100% correct on the reason for the buildup in the generator being insufficient water flow after a flush. Keep in mind this is the first time tearing into this thing since we bought the boat over three years ago so who knows how long it's been abused. I try and follow the plenty of water advice but not everyone who uses the boat is good about it.

And Dave, I have no doubt the Marine Elegance heads would be a nice upgrade, for the time being we are good with the VacuFlush system and it was far overdue for rebuilding so I don't feel the need to replace it. Parts are less than $200 for this fix. I'm curious to see how long it lasts before there is another issue.
 
I have recent Marine Elegance (fresh water flush) heads, new hoses. Because of persistent vent smell (no charcoal filter). I installed a Groco sweet tank 6 weeks ago. At the same time, I cleaned a lot of plaque like material from the bottom of the tank. Instead of losing the smells within 2 hrs as some suggested. I now have a constant smell from the vent. If the BR window is open, now the smell wafts back in if the wind is on the STBD bow. Frustrating.

I suggest you talk with Groco tech support to learn why their Sweet Tank is performing as advertised....they're very helpful! 410-604-3800.

--Peggie
 
If you have sludge at the bottom of your holding tank, based on our actual experience with the same issue, I recommend using Just Science (formerly called Forget About It) probiotic holding tank treatment. We've been using it regularly for 8 years now.

A few years ago I wrote a blog about our experience and how it made our holding tank "bigger" (not to mention better smelling):

https://www.pacificnwboatertested.c...get-about-it-holding-tank-probiotic-treatment
 
If you have sludge at the bottom of your holding tank, based on our actual experience with the same issue, I recommend using Just Science (formerly called Forget About It) probiotic holding tank treatment. We've been using it regularly for 8 years now.

A few years ago I wrote a blog about our experience and how it made our holding tank "bigger" (not to mention better smelling):

https://www.pacificnwboatertested.c...get-about-it-holding-tank-probiotic-treatment
Can anyone explain what this is any why it works?
I understand Peggie's explanation of aerobic vs anaerobi but I think folks are saying this works in an anaerobic environment... why? Or is that just marketing speak?
Every head chemical has marketing claims that it is the best thing since sliced bread... I usually ask... what is it any why is does it work better?
 
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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!!
 
Vent filters pretty much stop air flow in and out of the tank so they promote anaerobic bacteria which is what smells. Adding a vent just masks the problem. Getting air into the tank is usually the solution to the smell issue since aerobic bacteria doesn’t smell.
 
Now that it's been about 2 months with the aeration setup, I figured it's time for an update. Even after a few pumpouts and flushing the tank and vent out (although I haven't done a full cleaning and there's definitely a bit of scum on the sides), it's not perfect.

When we're in pretty calm sea states, the vent doesn't put out much odor. It's just a very slight smell that's somewhere between sour and earthy (only noticeable right next to the vent or in light winds blowing just the right direction). That's not too bad and we could live with it. It's nothing like the stink that came out of the vent when flushing before the aerator.

But any time we're in slightly rougher seas or take enough wakes at anchor and stir the tank up significantly, then it gets noticeably more smelly for a few hours to a day. After the last round of flushing it doesn't seem to be quite as bad and the smell does settle down faster afterward.

At this point I think the plan is to flush the tank out really well before we haul for winter (in another 6 weeks) and then over the winter I'll go over the aerator setup (both the tubing setup and the aerator bar in the tank) and see what I can do to get more flow. I think more holes in the aerator bar and some changes to the tubing setup from the air pump may allow me to pump more air into the tank. I may end up adding a second aerator bar at the other end of the tank with the goal of getting bubbling and agitation over a larger part of the tank instead of adding more holes to the existing aerator bar.
 
Or, you could do away with the black tank and hoses and install a composting/desiccating toilet. My boat had smell issues before, but now it doesn’t.

If you have a two head boat maybe convert one head to a composter for solids, and keep one head for urine only. A urine only tank will not smell nearly as bad as a urine and solid combination, and then your male guests can stand up to pee like real men! [emoji51]
 
Are you running the aerator 24/7 even when no one is aboard? That's essential to the success of aerators 'cuz without added air the tank contents become anaerobic, so the aerator has to spend the first hour or more after you turn it on restoring an aerobic environment.

Air needs to be distributed all the way across the tank...an aerator "bar" limits the distribution unless you can run some "perforated" tubing off it.


Replacing the "vent" thru-hull with an open bulkhead fitting should help, plus it allows you to put a hose nozzle against it to backflush the vent line every time you wash the boat and/or pump out. Anything that's tried to set up housekeeping in it will just get a water slide ride into the tank. However, you would not be able to do this if there's a vent filter in the vent line because vent filters are immediately "toast" if they get wet...the charcoal--even granular--will swell and block the vent line.

--Peggie
 
Are you running the aerator 24/7 even when no one is aboard? That's essential to the success of aerators 'cuz without added air the tank contents become anaerobic, so the aerator has to spend the first hour or more after you turn it on restoring an aerobic environment.

Air needs to be distributed all the way across the tank...an aerator "bar" limits the distribution unless you can run some "perforated" tubing off it.


Replacing the "vent" thru-hull with an open bulkhead fitting should help, plus it allows you to put a hose nozzle against it to backflush the vent line every time you wash the boat and/or pump out. Anything that's tried to set up housekeeping in it will just get a water slide ride into the tank. However, you would not be able to do this if there's a vent filter in the vent line because vent filters are immediately "toast" if they get wet...the charcoal--even granular--will swell and block the vent line.

--Peggie

The aerator has been running 24/7 for about 2 months since install. The aerator "bar" is an L shaped tube going into the tank. It goes straight down starting in one corner (at the opposite end from the vent), then turns 90* and runs across the tank for about 18" (angled forward and slightly diagonally across the tank) with perforations along the horizontal part (which is about an inch above the tank bottom). I've confirmed it's bubbling nicely along the whole length of the tube. The tank is 51" long, so that's why I'm thinking I may need to add a second aerator tube towards the other end of the tank to get air distributed through more of the tank and so the bubbling agitates more of the tank contents. The current bubbling is pretty vigorous, as it's visible through the tank sides with a flashlight and you can hear it bubbling as soon as the engine room hatch is opened.

The vent is a 1" vent hose (about 7 feet long) to an open mushroom thru hull (no filter). There's definitely a slight flow of air out of the vent from the aerator pumping into the tank and no issues with flushing or pumpout, so the vent shouldn't be an issue.

What I find interesting is that the waste level in the tank seems to have no effect on smell, and it's consistently worse after agitation, then settles back down. The steady state doesn't smell anaerobic (nor is it a particularly offensive smell). I think I might be the only person who actually notices it, although others have definitely noticed the smell after the tank has been agitated.

Adding a heavy dose of KO to the tank does help the smell a little bit, but it's not a drastic improvement over nothing. I've also tried adding sodium percarbonate to see if more oxygen helps, and it has basically no effect on the steady state smell, although it does help settle the smell down a bit faster after the tank has been stirred up. That makes me think the bit of stuff caked onto the tank walls may be contributing to the issue (there's no significant sludge at the bottom of the tank).

Any ideas to break up the junk on the tank walls would be appreciated, especially if I can avoid having to make multiple trips to the pumpout dock (and pay for multiple pumpouts) to be able to do the full OC Diver style tank cleaning. I've seen mention on RV sites of using Dawn dish soap to break up the fats in tank deposits and help them dissolve, but I'm not sure how effective it actually is (or if adding enough would cause a serious tank foaming problem).
 
Cleaning the tank walls is certainly a good idea, but that won't solve your odor problem. After reading everything you've posted, I suspect that your aerator isn't supplying enough air. A more powerful pump--but not TOO much larger--should solve the problem.



--Peggie
 
Cleaning the tank walls is certainly a good idea, but that won't solve your odor problem. After reading everything you've posted, I suspect that your aerator isn't supplying enough air. A more powerful pump--but not TOO much larger--should solve the problem.



--Peggie


A few changes to the air lines and either adding a second aerator bar into the tank or adding more holes to the current one should get me some more flow even with the current pump (the current setup is definitely restricting flow below what the pump can do with less back pressure). So I'll have to give that a try and see what happens.
 
Is there a chance that rough seas cause some liquid to enter the vent, causing back pressure and reducing the aerator flow/ effectiveness? This would be a result of a low spit in the vent line. If you can view it, confirm its straight / upward sloping it would rule that out. Can you reach the vent to confirm out flow when you experience the odor.
I would try Ted's cleaning regime at each pump out yo see if wall sludge is lessening & odor getting any less each time?
 
Is there a chance that rough seas cause some liquid to enter the vent, causing back pressure and reducing the aerator flow/ effectiveness? This would be a result of a low spit in the vent line. If you can view it, confirm its straight / upward sloping it would rule that out. Can you reach the vent to confirm out flow when you experience the odor.
I would try Ted's cleaning regime at each pump out yo see if wall sludge is lessening & odor getting any less each time?


I've confirmed there's no low spots in the vent (and spraying water into the vent with a hose doesn't trigger the odor problem or stop the outflow of air). The vent line was re-done and up-sized to 1" last winter, so I know there aren't any hidden surprises.

I think at this point I'm going to have to try some cleaning and also see if I can get a bit more air into the tank (the pump should be big enough, as it's the same one used in your thread on this from years ago). It has to be some combination of sludge in the tank and maybe not enough air. Although it never quite gets to zero smell even after sitting for a few days with no additions to the tank and no significant boat movement.
 
Never let the perfect become the enemy of the good - :)

I'll be happy if I can lower the stink to 10% of what it is now. Like a fart in the wind instead of down wind of a half moon door open pit outhouse.
 
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