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Old 15-04-2017, 09:58   #1
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drill and tap holding tank

I have the usual polyethylene holding tank. I believe that the aerobic reaction necessary to break down the black water is inhibited by the lack of fresh air in the tank, resulting in stinky vent syndrome. I propose to install and aquarium pump to feed clean fresh air into the tank, in the same way sewage processing systems have aerator pumps. My problem is, the tank only has one vent. How safe would it be to drill and tap a 1/4" NTP fitting into the top of the tank? If I bedded it with 5200, would it likely be safe enough or would I be condemning the tank.
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Old 15-04-2017, 12:00   #2
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Re: drill and tap holding tank

1. Neither 5200 nor any other sealant will bond permanently to PE. Seal it with rubber gasket and screws.

2. A baitwell aerator will work better than an aquarium pump, plus those are 12v pumps. Every aquarium pump I've ever seen needs 115vAC. However, how well either will work depends on the length of your vent line and how straight it is. In fact, you might not even need the aerator if you replace your 5/8" vent line with a 1" line (easy to do using a li'l gadget called the Uniseal UNISEAL), shorten and straighten it, and replace the vent thru-hull with an open bulkhead thru-hull.

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Old 15-04-2017, 14:39   #3
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Re: drill and tap holding tank

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1. Neither 5200 nor any other sealant will bond permanently to PE. Seal it with rubber gasket and screws
I'm going to be tapping the PE, so there will be a 1/4" NTP thread. I thought 5200 might add a little strength but probably not.
I bought a baitwell aerator pump and a cycle timer. I don't want it to run continuously, probably one minute in ten would suffice.

I bought and read your book, excellent source of information. I like the idea of forced aeration versus a larger vent line, it is a pretty long line. And it's an interesting experiment.
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Old 15-04-2017, 15:15   #4
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Re: drill and tap holding tank

For odor control only, you won't need anything thing like 24-hour aeration, so I would look for a timer. A few hours should be enough--you're not trying to do sewage treatment.

Avoid over tightening the fitting--a crack may appear some months from now. PE is prone to that. Just finger tight with some Teflon tape should be plenty.

I would go with the bigger vent. Much simpler. I've tested both. In my opinion, aeration should be reserved for really big tanks, deep in the bilge, where nothing else works. I suspect you will loose interest in the experiment after a while and yearn for simplicity. I assume you've tried a nitrate-based treatment, like Oderlos, or No Flex? That might be enough.
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Old 15-04-2017, 15:34   #5
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Re: drill and tap holding tank

I assume you have a stink coming out of the vent only when you flush said unit and expel some air from the tank.

Will not pumping air in and then being expelled out the vent only exacerbate the issue.

As others have said it is a holding tank not a treatment system.
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Old 16-04-2017, 05:25   #6
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drill and tap holding tank

Listen to Peg!!! The uniseal will work, tapping will not because the 3/8" of tank isn't thick enough (which is why they always weld bosses on where threads are

Uniseals are amazing!
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Old 16-04-2017, 06:25   #7
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Re: drill and tap holding tank

Assuming you could get the tank clean enough so that a shop would work on it, would it be possible to have a fitting added for this? Particularly one with some extra reinforcement around it. Or barring that, what about DIY bonding on a doubler plate, & then tapping things for a fitting? Or bonding on a doubler plate that included a fitting? Since bonding to PE is discussed in a fair bit of literature on epoxy.
https://www.jamestowndistributors.co...t.do?docId=420

I'd put up a link to the WEST System site, but for some reason it's not working at the moment.
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Old 16-04-2017, 06:29   #8
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Re: drill and tap holding tank

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Will not pumping air in and then being expelled out the vent only exacerbate the issue..
As Peggy explains in her book, fresh air enables aerobic digestion which does not smell. Anerobic bacteria results in hydrogen sulphide which smells. That's the science behind my idea.
Aerobic digestion is what treatment plants use, that's all they are. I have installed and serviced treatment plants in homes and businesses and all they are is a air pump bulling air into the mix to help it break down. Although we will discharge the mix, it's best if it does not produce H2S)4 via anaerobic activity. That's all I am trying to do, bet it works. I'm going to do it, the pump and cycle timer have been ordered, I will report on success.
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Old 16-04-2017, 06:34   #9
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Re: drill and tap holding tank

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I suspect you will loose interest in the experiment after a while and yearn for simplicity.
No, I'm a geek, I love experiments, especially if there is a chance of solving a real life problem. The boat is a fun science lab, I'm adding energy meters on everything, a electronic refrigeration controller, solar water heating, anchor watch via SMS, all kinds of fun stuff. My house is another experiment, we are off grid, had an electric car, I built an energy management system for the loads, I love this type of projects.
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Old 16-04-2017, 06:35   #10
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Re: drill and tap holding tank

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easy to do using a li'l gadget called the Uniseal
I'm not understanding the Uniseal, what is the purpose?
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Old 16-04-2017, 06:42   #11
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Re: drill and tap holding tank

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easy to do using a li'l gadget called the Uniseal
Reading the information, the Uniseal would mean drilling a larger hole in the holding tank, relying on the Uniseal to seal it? Do you think it is better than a threaded hole? I would think a 1/4" threaded hole would be so small that the thread depth ratio would be adequate.
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Old 16-04-2017, 06:50   #12
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Re: drill and tap holding tank

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Assuming you could get the tank clean enough so that a shop would work on it, would it be possible to have a fitting added for this?
I could absolutely get it clean enough, muriatic acid will dissolve the calcium that has built up in it, once the fittings have been removed. That would be easy this hurricane haul out. I am the shop, I would do that myself. I think I could get fingers inside the inlet port and back the new port adapter plate with nuts.
Another way would be to use four self tappers around a plate with a bulkhead fitting, I could fabricate from a brass 1/4" adapter and a brass plate, brazing the adapter to the plate. A rubber gasket would provide a seal.
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Old 16-04-2017, 06:51   #13
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Re: drill and tap holding tank

Wouldn't it be much easier to just add a charcoal odor filter to your vent like everyone else?
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Old 16-04-2017, 07:00   #14
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Re: drill and tap holding tank

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No, I'm a geek, I love experiments, especially if there is a chance of solving a real life problem. The boat is a fun science lab, I'm adding energy meters on everything, a electronic refrigeration controller, solar water heating, anchor watch via SMS, all kinds of fun stuff. My house is another experiment, we are off grid, had an electric car, I built an energy management system for the loads, I love this type of projects.
Yeah, I 100% get that. I've probably got 20 projects in-process at any time.

In that case, you need to look into water filtration/treatment + rainwater collection as a pair. I've switched to rain, since the marina is sulfurous and hard.
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Old 16-04-2017, 07:23   #15
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Re: drill and tap holding tank

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Reading the information, the Uniseal would mean drilling a larger hole in the holding tank, relying on the Uniseal to seal it? Do you think it is better than a threaded hole? I would think a 1/4" threaded hole would be so small that the thread depth ratio would be adequate.
The tank wall is too thin to tap successfully...you're risking a cracked tank. The Uniseal doesn't leak and is available as small as 3/16".

You might also want to take a look at the Groco Sweettank installation instructions which you can download from here Groco Sweetank (click on the "download" link at the right of the page) for some guidance on how to run the piping inside the tank to insure that air is distributed throughout the tank, not just a column of air.


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