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Old 11-01-2018, 09:07   #1
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Flexible gravity-drain holding tanks

Hi All,

Curious to hear some input here. I have a traditional below-the-waterline hard holding tank on my boat. After a ton of going back and forth about what to do with this system that I despise, I've finally decided that I want to do a small, gravity-drain holding tank behind each of my two heads that I can open when I'm at sea. I can do this using my current toilet through hulls.

I have good space above the water line behind the aft head, but less in the forward - the shape of the hull tapers this space considerably as you go forward. See pics below.

I am looking at small Nauta tanks.

Can I also plumb these holding tanks to a deck waste output in case I'm in a harbour for a while and want a pump out?

Any thoughts appreciated. Also, I know I should get rid of that tap valve in the background.... I promise I will.
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Old 11-01-2018, 12:04   #2
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Re: Flexible gravity-drain holding tanks

Flex holding tanks = yuck

They permeate readily.

Make a cardboard mock-up and have ronco or similar build a poly tank.
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Old 11-01-2018, 12:16   #3
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Re: Flexible gravity-drain holding tanks

Cool. Thanks Sailmonkey. Didn't realize there was such a thing as custom plastic holding tanks. I'm going to get some quotes...
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Old 11-01-2018, 12:34   #4
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Re: Flexible gravity-drain holding tanks

Quote:
Originally Posted by Peregrine1983 View Post
Cool. Thanks Sailmonkey. Didn't realize there was such a thing as custom plastic holding tanks. I'm going to get some quotes...
I don't think you'll have to resort to a true "custom" tank... Ronco Plastics Ronco Plastics marine Tanks makes TOP quality thick-walled rotomolded PE water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular (which means you might be able to fit a larger one in the same space), and they install fittings in the sizes and locations specified by the customer when they make the tank.

Note that you're not limited to the orientation shown in the drawings...tanks can be oriented any direction 'cuz there is no top or bottom before the fittings go in and you decide where they go. So rotate, flip end for end, whatever... For your purposes, putting the point of a triangle on the bottom with the discharge as close to it as possible would prob'ly work best 'cuz it eliminates a flat bottom on which sludge can collect.

Try not to put the tank any higher than you absolutely have to...'cuz the taller it is, the longer a straight up line from the toilet the top of the tank has to be.

If you have to go with a custom tank, they'd have to make the mold, which would be prohibitively expensive. In which case, your best source would be Triple M Plastics Triple M Plastic Products Inc They make top quality custom welded tanks. A good bit more expensive than a rotomolded tank for which the mold already exists, but worth the price if it's the only thing that'll work.

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Old 11-01-2018, 12:41   #5
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Re: Flexible gravity-drain holding tanks

Awesome. I was really hoping you'd see my post and chime in. You rock Peggie.

Thank you.
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Old 11-01-2018, 15:29   #6
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Re: Flexible gravity-drain holding tanks

Always glad to help when I can.
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Old 11-01-2018, 17:21   #7
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Re: Flexible gravity-drain holding tanks

I can vouch for triple M plastics, I sent them a drawing of my holding tank and they built exactly what was drawn, and of course it fit perfectly. They were on time and exactly on their price quote.
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Old 11-01-2018, 19:06   #8
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Re: Flexible gravity-drain holding tanks

If you hate holding tanks in general composting heads are all the rage.

Not something Iím into, but everyone Iíve talked to with one LOVES THEM
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Old 12-01-2018, 08:05   #9
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Re: Flexible gravity-drain holding tanks

Thanks Futurestories. I've just heard too many mixed reviews and horror stories. My current holding tank setup has already gotten me about as closely acquainted with excrement as I ever want to get.
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