Holding Tank Ventilation

[Tedd]

I'm posting this in Trailer Sailors because it's probably not relevant for most non trailer sailors.

Following some advice in @Peggie Hall HeadMistress 's book, that it's important to have plenty of oxygen in the holding tank, I decided to make a ventilation system. It turns out that the deck fitting is 1-1/4 NPT, so, I was able to thread an in-line valve I had left over from another project into an standard NTP plug and bond an air-line fitting into it. Now, whenever I'm done with my compressor, I just plug in the line and let it exhaust through the holding tank. The valve allows me to regulate the flow to ensure the tank isn't over pressurized. Since not everyone will have a nice little valve like this lying around, you could achieve the same thing (safer, even) by dialing down the regulator on the compressor before you hook it up, so that it can barely put out any pressure. Or, you could fill the air-line fitting with epoxy and drill a small hole through it, to regulate the flow.

Always check the holding tank exhaust when you do this to ensure that the air is flowing freely!

 

[Don S/V ILLusion]

Please explain.
if the tank isn’t vented, how does this provide ventilation?

 

[Tedd]

Please explain.
if the tank isn’t vented, how does this provide ventilation?

Sorry, I probably should have provided more context about the advice in @Peggie Hall HeadMistress 's book.

The holding tank has both aerobic and anaerobic bacteria in it. The anaerobic bacteria smells but the aerobic bacteria doesn't. If there's enough oxygen in the tank, then the aerobic bacterial will out-compete the anaerobic bacteria and you won't have smell. I wanted to ensure that there would always be enough oxygen in the tank to keep the aerobic bacteria winning, hence the idea of adding fresh air once in a while.

 

[Don S/V ILLusion]

Sorry, I probably should have provided more context about the advice in @Peggie Hall HeadMistress 's book.

The holding tank has both aerobic and anaerobic bacteria in it. The anaerobic bacteria smells but the aerobic bacteria doesn't. If there's enough oxygen in the tank, then the aerobic bacterial will out-compete the anaerobic bacteria and you won't have smell. I wanted to ensure that there would always be enough oxygen in the tank to keep the aerobic bacteria winning, hence the idea of adding fresh air once in a while.

Yes, I know. What I was referring to is the free space in the already vented tank which is exposed to air and why adding more air into the ventilated tank would make any difference. That’s one of the purposes of the vent line.maybe I should direct this to whomever gave you that advice.

 

[Peggie Hall HeadMistress]

Hi Tedd... I'm glad you not only bought my book, but have actually read at least some parts of it. I'm also impressed that you've totally grasped the need for aerobic conditions in a holding tank. But your "ventilation system" can't work for a couple of reasons, starting with: 1: You failed to include a tank VENT. Your inline valve is only a pressure relief valve, it doesn't actually vent the the tank...that has to happen above the surface unless the tank contents are aerated.
2. Adding "shots" of air once in while can't keep a tank aerobic...that requires a continuous flow of air 24/7/365 except during winter or other extended layup. The instructions for the Groco Sweettank aerator will help you understand all this...Groco removed 'em from their website, but I have a PDF I'll be glad to send you if you'll send me a PM that includes your email address (no way to attach anything to PM).

Your "ventilattion system" was good try...you had all the principles right, execution just fell a bit short. I have a few of those "ingenius ideas" tucked away in my own attic. So keep thinking and trying new ideas...and I''ll be glad to let you bounce any of 'em off me.

-Peggie

 

[Tedd]

Thanks for the reply, @Peggie Hall HeadMistress . I feel like I may not have explained my system very well. The valve is not a pressure relief valve, it's merely there to control the flow through the tank and ensure that the tank isn't exposed to too much pressure. If I leave the compressor on it will, as you described, result in continuous flow of fresh air through the tank, 24/7. It had not been my intention to do that because I didn't think it was necessary. But if you say it is there's no reason I can't do that.

 

[Peggie Hall HeadMistress]

All tank vents--fuel, water and waste-- have two functions: to provide an escape for air displaced by incoming contents and a source of air to replace contents as they're drawn out. Your valve--at least I'm guessing that's what your photo is--is installed in the deck pumpout fitting which has one end of a hose connected to it and the other end connected to the tank discharge fitting. So I don't know how any air introduced into it can get into the tank Nor, without a tank vent, how any of the compressed air can escape.

--Peggie

 

[Apex]

waste treatment plants will do the same: We made micro perforated bladders that would be installed over pipes. The micro perforations would bleed air under the surface of the settling pond. I assume the tank IS VENTED, as most tanks are. By adding air into the pumpout (which has the pickup tube very near the BOTTOM of the tank, the OP is blowing air through the effluent, much like a kid blowing bubbles in milk glass with a straw. Just a much messier froth is formed.

Share specs on air pressure used, and if that has seemed to help: the flow will need to be low enough to prevent over pressure (vent can keep up with the air added into the system, AND toilet/joker valve are not over-challenged for pressure) and also not create an over-froth situation creating mess in the vent lines that would further restrict natural ventilation.

The bigger question, is if the tank is properly vented with 1" pipe per Peggy recommendations, that should be adequate and thus is aerating the tank necessary?

 

[Don S/V ILLusion]

waste treatment plants will do the same:

Same principle, different reason.

Sewage treatment plants have effluent limits to preserve water quality and aeration is a primary means of bacterial decomposition to achieve effluent limits.

What we are concerned with here is minimizing odor accomplished simply by ensuring the free space in a holding tank is ventilated.

 

[Tedd]

Hi @Peggie Hall HeadMistress ,

I knew there had to be something important missing from my explanation, to cause all this confusion, but it took a while before the light went on. This system is only intended to work when the holding tank is empty. I always pump out the tank before I put the boat on the trailer to bring it home. At home, the tank is empty.

You're quite right that this system will not work when the tank has a significant amount of effluent in it, and it's not designed to. I posted it here in Trailor Sailors specifically because it's not something that will be useful in the more typical situation where the holding tank normally has effluent in it.

The idea was to have a system for ventilating the empty holding tank that's cheap ($2 plus found material) and easy (~10 minutes work).

 

[THECUSCUS]

Forcing air into the tank, I see the potential for a nasty mishap

 

[Tedd]

Forcing air into the tank, I see the potential for a nasty mishap

Exactly. As I said in my initial post, it's important to do this with care. There are several ways to ensure that the tank isn't over-pressured, the simplest being the method used by aircraft mechanics to leak test tanks: You put a balloon in the line, which acts a pressure "fuse." Since I don't leave mine unattended I haven't done that yet. I can easily determine that the tank isn't over-pressured just by monitoring the vent line. But if, as @Peggie Hall HeadMistress suggested, I leave it running continuously, then I will definitely put some kind of automatic over-pressure protection into the system.

 

[Don S/V ILLusion]

Hi @Peggie Hall HeadMistress ,

I knew there had to be something important missing from my explanation, to cause all this confusion, but it took a while before the light went on. This system is only intended to work when the holding tank is empty. I always pump out the tank before I put the boat on the trailer to bring it home. At home, the tank is empty.

You're quite right that this system will not work when the tank has a significant amount of effluent in it, and it's not designed to. I posted it here in Trailor Sailors specifically because it's not something that will be useful in the more typical situation where the holding tank normally has effluent in it.

The idea was to have a system for ventilating the empty holding tank that's cheap ($2 plus found material) and easy (~10 minutes work).

This sounds like a solution to a non-existent problem. An empty tank doesn’t have anything in it to be aerated.

 

[Johnb]

A German friend who has a RV showed me how his holding tank system works and in summary by bubbling air through the contents it obviates the need for chemicals.

Seems to me that gently bubbling air back through the pump out, the end of which is under or at least in water, to then exhaust through the vent, is a good idea.

Maybe we should re read Tedd’s posts and truly understand.

 

[Peggie Hall HeadMistress]

I agree with Don...you've created a solution to a problem that doesn't exist...worse yet, it's a solution that can do some damage to the tank and sanitation system.

Tedd, you've said several times that you created this "ventilation system" following advice in my book. I need to make it very clear that I did NOT advise doing anything like what you've done, nor would I ever do so.

--Peggie

 

[Peggie Hall HeadMistress]

Maybe we should re read Tedd’s posts and truly understand./QUOTE]

You might want to re-read post #10.

Aeration has long been an accepted way to prevent holding tank odor. However, there must be waste in the tank TO aerate.

--Peggie

 

[Tedd]

Tedd, you've said several times that you created this "ventilation system" following advice in my book. I need to make it very clear that I did NOT advise doing anything like what you've done, nor would I ever do so.

--Peggie

Hi @Peggie Hall HeadMistress ,

The advice from your book that I was referring to was the desirability of having sufficient oxygen in the holding tank to encourage the growth of aerobic bacteria. I'm genuinely sorry that I wasn't more specific about that in my original post, and more specific about how the system is intended to be used.

 

[MikeHoncho]

Hi @Peggie Hall HeadMistress ,

The advice from your book that I was referring to was the desirability of having sufficient oxygen in the holding tank to encourage the growth of aerobic bacteria. I'm genuinely sorry that I wasn't more specific about that in my original post, and more specific about how the system is intended to be used.

You were absolutely clear abou this in your first post and no apologies should be needed to coddle the egos of others………