DIY Holding Tank aerator.

[dhays]

Someone asked me about the holding tank bubbler that I made for the boat. I thought I would describe it here.

The concept is simple, for someone simple minded like me. The basic idea is to add oxygen in the holding tank to promote the growth of aerobic bacteria and reduce the population of anaerobic organisms. The idea is that aerobic organisms don’t stink. Anaerobic do.I got the idea originally from Don of Bacchus who helped a lot with questions.

My holding tank had a 3” round access hole in the top that was used to hold the three float sensors for my holding tank level indicators. Rather than cut another hole in the tank, I decided to use this opening for the aerator. I got a blank 3” inspection port cap and epoxied a 1/2” PVC fitting through a hole that I drilled into the cap. I then attached a brass threaded fitting into that and used reducers to attach a barbed nipple. I had to play around a lot in Home Depot to figure out the parts, but it was all pretty cheap.

I then used 1/2” PVP pipe to create a simple L shaped pipe. The idea is that it will run straight down into the tank and then run along the bottom. The end of it it was capped and small holes were drilled along its length and in the end cap. This was cemented to the cap that I made above.

To provide the air for the aerator, I bought a Marine Metal 12v bait tank aerator. It is designed for two tanks so has to air outputs and a couple of stone bubblers and 1/4” hose. It also comes with the T fitting so both air outputs can be combined into one air stream. This is what I did.

The cap and pipe assembly was fitted into the tank. The air hose from the aerator was attached to the hose barb at the top of the cap, and the 12 air pump was wired into a convenient 12v power source. I used my shower sump pump circuit.

Poor description on my part but here are the only photos that I have.

 

[Dougcole]

Looks good. Thanks for posting.


These kind of projects are always so hard to describe, but easy to understand with pics.

 

[HeadMistress]

Very clever! However, urine will "eat" the brass fittings, so keep an eye on them and replace with PVC or marelon when you see the first signs of damage. It shouldn't be too hard to keep an eye on them because--as Groco learned the hard way, forcing them come up with a design that still requires cleaning, but not nearly as often--sludge will clog the holes in the piping across the bottom, requiring at least annual removal to clean it. The maintenance portion of their Sweettank system instructions should be useful Groco Sweet Tank




--Peggie

 

[Lou_tribal]

I am still looking to understand why urine would damage any metal. It is not acidic but near neutral if not neutral in pH. Is it a chemical reaction between its component and metals? If yes what component?
Just would like to understand for my own knowledge.

L

 

[DavidM]

I haven't measured the pH of urine, but I do know it contains uric acid which reacts with Ca and Mg compounds in sea water to form scale in your waste lines.

I am sure that uric acid is corrosive to some extent.

David

 

[dhays]

Very clever! However, urine will "eat" the brass fittings, so keep an eye on them and replace with PVC or marelon when you see the first signs of damage. It shouldn't be too hard to keep an eye on them because--as Groco learned the hard way, forcing them come up with a design that still requires cleaning, but not nearly as often--sludge will clog the holes in the piping across the bottom, requiring at least annual removal to clean it. The maintenance portion of their Sweettank system instructions should be useful Groco Sweet Tank

Thanks for the link.

I can’t take credit for the “clever” part, that was Don from Bacchus. I don’t expect any corrosion issues. The metal fitting are all above the tank. The only fittings actually in the tank are PVC.

I also wasn’t very clear but the inspection port is located on the top of the holding tank. So unless I really screw up and fill the tank completely, those metal fittings won’t come into contact with the holding tank contents.

I have wondered about the holes becoming clogged but didn’t think it would end up being a problem. Partly because there is always positive pressure forcing air out through those holes. I’ll pull it out and check it and let you know.

 

[dhays]

I am still looking to understand why urine would damage any metal. It is not acidic but near neutral if not neutral in pH. Is it a chemical reaction between its component and metals? If yes what component?
Just would like to understand for my own knowledge.

L

Peggie will give us the correct answer, but I believe it is is the urea in the urine that causes the corrosion issues. I don’t think it is is urea per se, but some of the other forms of urea that will occur once it is excreted.

 

[dhays]

Here are some more photos. The pump is just zip ties into position and hasn't moved at all. Notice also the kluge where the air line enters the tank. To avoid kinking the air line, I zip ties it to a rubber washer that controls the radius of bend.

 

[Bacchus]

Dave
Nice work and hope it is working as well as ours.
Credit to Peggie for teaching us the science / biology.
The creativity is just adapting the principle to individual tanks.
I truly am surprised at the durability of that inexpensive air pump.

 

[Comodave]

Yes, getting air into the holding tank will do wonders for getting rid of the smells. Metal in a holding tank, or a metal holding tank isn’t a good idea. We looked at a very high quality boat that was getting it’s aluminum holding tank replaced since it was like a colander and leaking badly, plus the associated smells and mess.

 

[Lepke]

I knew someone that made remote site sewage systems. It was like a septic tank, had a couple sections and used an aquarium like pump to add air. It didn't require a drain field because clear clean water came out of the tank. It was tested for a year in NW Oregon about 35 years ago.

 

[dhays]

Dave
Nice work and hope it is working as well as ours.
Credit to Peggie for teaching us the science / biology.
The creativity is just adapting the principle to individual tanks.
I truly am surprised at the durability of that inexpensive air pump.

Really is working well. I’m encouraged by how long your pump has been working.

What I did was based on what you did ahead of me. Yes, Peggie has been an invaluable resource.

 

[HeadMistress]

I knew someone that made remote site sewage systems. It was like a septic tank, had a couple sections and used an aquarium like pump to add air. It didn't require a drain field because clear clean water came out of the tank. It was tested for a year in NW Oregon about 35 years ago.

Quite a few business installed mini sewage treatment plants in the '90s...Ben and Jerry's Ice Cream plant was the most famous, but a number of golf courses in the arid regions of the country did and even a few marinas who couldn't install septic tanks and had to rely on pumper trucks to empty their holding tank collection tanks. They consisted of a "treatment plant" about the size of a single car garage, that was layered with rocks, sand etc as filtration and specific types of vegetation to supply oxygen. Toilets, kitchen and bathroom sinks--just about everything with a drain were rerouted to go into 'em and be recycled for toilet flushing, car--and boat--washing, grounds watering etc...'cuz the output was clean enough to re-use for anything but potable water. They were the hottest thing in private sewage treatment for a while, then fell off the "public radar." I have no idea how many of 'em are still in operation, if any.


--Peggie

 

[rwidman]

I have often thought that forcing air down the pumpout fitting would aerate the holding tank. Not something that you might use while underway, but if the boat sits in a marina for weeks or months at a time.

I've never tried it though, using a treatment product seems to control any odors.

 

[rwidman]

To avoid kinking the air line, I zip ties it to a rubber washer that controls the radius of bend.

Home centers sell a device for avoiding kinks in PEX tubing that would work well for this.

 

[guy with a boat]

I have often thought that forcing air down the pumpout fitting would aerate the holding tank. Not something that you might use while underway, but if the boat sits in a marina for weeks or months at a time.

I've never tried it though, using a treatment product seems to control any odors.

That seems like a great idea.

Just going from memory of the plumbing, it seems like you could put the air hose into the side of the pumpout line above the tank and pressurize it slightly at that point. As long as the pumpout line doesn’t have any air leaks, it should feed air into the bottom of the tank. The air distribution would only be from a single point, but the simplicity of the installation and lack of maintenance requirements might offset that. Seems promising.

Peggie?

 

[HeadMistress]

That would only create a leak in the pumpout line that's also likely to prevent pumpout from achieving a vacuum.


--Peggie

 

[Comodave]

I am not sure I would want to pressurize the pump out hose. Last thing I would want to do is blow that hose off the holding tank and then dump the contents into the bilge. Probably not too likely but I wouldn’t take that chance.

 

[dhays]

Home centers sell a device for avoiding kinks in PEX tubing that would work well for this.

I’ll have to look for that. Would probably work better than my kludged solution.

 

[Comodave]

Hose benders, but they are usually for larger pipe, at least the ones I have used.

 

[rwidman]

That would only create a leak in the pumpout line that's also likely to prevent pumpout from achieving a vacuum.


--Peggie

The pump would be attached to a spare cap. Or replace the cap. It would be removed for a pumpout.

 

[TrawlerAJ]

No reason you couldn't put an air fitting on a spare deck cap - if the vent is working properly, the pump out hose will fill with air and glug into the holding tank. But if your holding tank would benefit from a bubbler, if vents aren't all that effective, then a more permanent installation would be a lot less aggravation over time! I'd immediately break a toe on that air fitting, or trip over the air line, or forget to set it all up before I left, etc...


I recently installed a Bacchus system on my tank after several seasons of trying everything. I confirmed the vent hose wasn't blocked, but it's certainly too long to be effective. I utilized the same macerator port on my tank that Don used, but I didn't put anything inside the tank. Just got the necessary PVC and nylon fittings, and hooked a 110v Marine Metal bubbler up to the end. I installed bubbler on the back wall next to an unused Washer/Dryer outlet. It obviously only runs when we're on shore power, but for 99% of boats, that's 99% of the time. A 12v bubbler could have been hooked up to the macerator 12v power just as easily. A ball valve allows for maintenance of the pump and airline. I decided to leave the short hose coupler and macerator power in place, as I may decide to reinstall a macerator in the future. I boat in Great Lakes, but it's handy for flushing tank at the end of the season, and if this boat ever Loops, it'll be handy to have it installed. This setup, with no "bubble bar" actually in the tank, seems to have quelled our ongoing stink issue. I have some aquarium expertise, and learned a long time ago that the bubbles in the fish tank are pretty, but the oxygen exchange happens at the surface. The bubbles help with oxygenation in a fish tank because they keep the water moving around. I feel like the same thing applies here, at least in flat/shallow holding tanks. I'm hoping that good aerobic bacteria are thriving, but even if I'm just keeping a constant flow of fresh air to force out the stinks, well, it's working! Thanks to Don and Peggie, everyone onboard is happier now, as well as friends when we raft up!

 

[Mischief Managed]

This setup, with no "bubble bar" actually in the tank, seems to have quelled our ongoing stink issue. I have some aquarium expertise, and learned a long time ago that the bubbles in the fish tank are pretty, but the oxygen exchange happens at the surface. The bubbles help with oxygenation in a fish tank because they keep the water moving around. I feel like the same thing applies here, at least in flat/shallow holding tanks. I'm hoping that good aerobic bacteria are thriving, but even if I'm just keeping a constant flow of fresh air to force out the stinks, well, it's working! Thanks to Don and Peggie, everyone onboard is happier now, as well as friends when we raft up!

View attachment 119215

I was going to post about not really needing bubbles to oxygenate the water in the holding tank, but you beat me to it. I plan to add a T fitting between my vacuflush pump output and the tank. I will add air via the extra port on the T with an aquarium pump with two one-way valves inline so that sewage can never back up the air line. The added air will displace the air in the tank which will flow out the vent. I run my inverter all the time when underway or anchored, so the aquarium pump will always be running. They require very little power.

 

[Bacchus]

Brian
Glad its working and confirms my experience.
I dont think there is a lot of science or necessity to bubble its more that it gets O2 to the tank.
I may be wrong but if an adequate vent line works just pumping air to the top of the tank should work even better. Bubbling of any sort has to be even better.

 

[ronobrien]

I knew someone that made remote site sewage systems. It was like a septic tank, had a couple sections and used an aquarium like pump to add air. It didn't require a drain field because clear clean water came out of the tank. It was tested for a year in NW Oregon about 35 years ago.

These type systems are almost exclusive for use in the Caribbean. They use the outflow to water their gardens as water is in short supply down there.

 

[Martin J]

I recently added a 12v air pump to my holding tank. I used a aquarium / bait well pump, Air hose from the engine room to a brass flange in the top of the holding tank, Soldered a piece of 1/4" copper in to the bottom of the flange . The copper is "L" shaped and the end sealed. I drilled lots of 1/32" holes in the bottom of the "L tube" . Tested it in a bucket and streamed lots of bubbles no problem. In operation I smelt a increase of odor by the vent pipe. This disappeared after a couple of days. Now have "very good bacteria"!

 

[Bacchus]

I recently added a 12v air pump to my holding tank. I used a aquarium / bait well pump, Air hose from the engine room to a brass flange in the top of the holding tank, Soldered a piece of 1/4" copper in to the bottom of the flange . The copper is "L" shaped and the end sealed. I drilled lots of 1/32" holes in the bottom of the "L tube" . Tested it in a bucket and streamed lots of bubbles no problem. In operation I smelt a increase of odor by the vent pipe. This disappeared after a couple of days. Now have "very good bacteria"!

I started with a copper / brass? (Don't remember) but it corroded in one season. Switched to a small dia PVC tube and all is fine.

 

[Martin J]

I started with a copper / brass? (Don't remember) but it corroded in one season. Switched to a small dia PVC tube and all is fine.

That's interesting. I had copper pick up pipes in my last boat with no problem, They were 30 +years old when I had to replace them. I'll certainly monitor the pipe over the future and change it out when I detect corrosion. Thanks for the information.

 

[ronobrien]

I was wondering if your heads were FW or SW flush. As I am only familiar with land based septic systems, which are obviously FW flush, I thought perhaps the SW would effect the bacteria I am seeking to produce.
Thanks.

 

[Martin J]

Salt water flush.