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Old 05-11-2015, 02:43 PM   #1
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Re-purpose Holding Tank

I was talking to a friend yesterday that told me of an individual who has a SS blk water holding tank. He is installing new heads that don't require a holding tank. So he is gong to convert it to a fresh water tank.
Seems very risky to me, am I just to cautious with my health?
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Old 05-11-2015, 03:01 PM   #2
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Lol...no!
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Old 05-11-2015, 04:43 PM   #3
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Greetings,
Mr. mb. GREAT idea! Get your friend to take out a multi million $$ life insurance policy with YOU as the sole beneficiary. I figure you should be in the market for a Nordhavn within 6 months. Happy shopping.

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Old 05-11-2015, 05:12 PM   #4
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Anything can be sanitized safely, if still worried RO will usually do the trick.

Good enough for astronauts...
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Old 05-11-2015, 06:06 PM   #5
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Hmm! I don't think that the FDA would ever allow that in a food processing plant. But what the FDA will do and what a clever individual can do are two different things.

First clean and agitate the tank with detergent. Use a circulating pump and a spray wand like is used on RV black water tanks to get into all corners. Dump, rinse and do it again. Then go over every weld joint with a torch to heat the metal up to above boiling temp. Have an assistant follow up every so often with a drop of water to make sure it sizzles a few seconds after the torch passes. The welds are where bacteria can hide.

Then sanitize with a bleach solution. Bleach will attack aluminum so don't leave it there long, maybe a couple of hours. Whoops, it is SS so maybe overnight will be ok. Use a pretty strong solution, maybe a cup to 5 gallons of water. Dump the bleach solution and rinse thoroughly.

Then after all of that, I would drink from it, but only if it held 80+ proof booze ;-).

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Old 05-11-2015, 06:54 PM   #6
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Stainless isn't a great material for holding black water. It eventually develops pin hole leaks. Even if the tank isn't leaking now, I'd be afraid that what ever pitting is on the inside of the tank will hold bacteria. I would remove the stainless tank and replace it with a plastic tank.

Oh yeah, I forgot to say Ewww!
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Old 05-11-2015, 07:34 PM   #7
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Stainless isn't a great material for holding black water. It eventually develops pin hole leaks. Even if the tank isn't leaking now, I'd be afraid that what ever pitting is on the inside of the tank will hold bacteria. I would remove the stainless tank and replace it with a plastic tank.

Oh yeah, I forgot to say Ewww!
This was exactly my answer to my friend.
Also its not an easy removal, so sanitizing off the boat is not practical.
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Old 05-11-2015, 07:44 PM   #8
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Stainless is fine for a fresh water tank if that's all it's been. Our 1973 boat has it's original stainless water tanks and the water tastes like water. As opposed to boats I've been on with plastic water tanks where the water tasted like plastic. But it doesn't have to be this way; I've been on boats with plastic water tanks and the water tasted like water.

But to use a former blackwater tank as a fresh water tank, while technically feasible, why bother? Also, as Parks noted, stainless blackwater tanks start to corrode and eventually pinhole because of the contents. I know this because our boat had a stainless blackwater tank that did exactly this, so we replaced it with a plastic tank.

The risk, let alone the psychological disadvantage of knowing what your fresh water tank used to be, would seem to indicate that the smart solution is to replace the holding tank with another new stainless tank for fresh water or a plastic one.
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Old 05-11-2015, 08:33 PM   #9
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There's the scientific answer...and the emotional one.

And then, Parks may have answered the practical one
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Old 05-11-2015, 08:46 PM   #10
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There's the scientific answer...and the emotional one.

And then, Parks may have answered the practical one
Hey, and don't forget the "logical" one, that is, no need for an extra water pump at all......he can just pipe in the old mascerator! Great pressure at the shower head!
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Old 05-11-2015, 09:12 PM   #11
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He could use it for a fresh water flush head.
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Old 05-11-2015, 09:57 PM   #12
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He could use it for a fresh water flush head.
Nope, he's just installed a compost head, which is why he is converting the tank.
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Old 05-11-2015, 10:42 PM   #13
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I gotta go with Parks on this fix.
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Old 05-11-2015, 11:01 PM   #14
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I was talking to a friend yesterday that told me of an individual who has a SS blk water holding tank. He is installing new heads that don't require a holding tank.

And just what heads would those be??? 'Cuz I don't know of any except composters that wouldn't. And unless he's in the caribbean or other tropical/subtropic climate where the temps are always WELL above 70, he's likely to regret installing those.

So he is gong to convert it to a fresh water tank.

Don't even consider it, for several reasons....starting with, urine is so corrosive that it'll turn any metal tank--even 316 stainless into a colander within an average of about 10 years, start leaking at a weld (seam or fitting) in an average of about 5 years...so even if the tank is is only a few years old, it's already pitted and corroded, the only question is, how seriously. And...fresh water is chlorinated, which limits the average life of a metal water to tank to about 20 years...less if he's been adding a little bleach to each fill.

So what's he's gonna have is a damaged tank that he may or may not have been able to sanitize 100%...and he's gonna wash his face, wash his dishes, maybe even brush his teeth in water from that tank????

Do people have any idea how much water from their tanks they ingest even if they don't actually drink it? Wash your hands in it, then pick up a sandwich...rinse out a cup, then fill that cup with your "pure" bottled water...wash your dishes in it. Brush your teeth...Shower, or just wash your face, it gets on yr lips, in your eyes, in yr ears...

The good news is, he's gonna stop putting toilet waste into a metal tank before it starts leaking stinky stuff, which it's bound to do. Just a matter of when and what it will leak, not whether it will.
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Old 05-12-2015, 12:54 AM   #15
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I can see a time in the future when someone tells him

"dude your water tasts like shit"

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Old 05-12-2015, 01:13 AM   #16
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Good God Man! Only dumb animals eat or drink items contaminated with fecal matter. Is it worth one or two or even three (or more) "Boat-Dollar$" to take chances... I think NOT! Put in a nice new clean tank and kick the black water tank to the curb.

Like Parks said - - > EWWWWW!!!
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Old 05-12-2015, 07:11 AM   #17
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A good set of roofing sheers will usually handle tank wall material.

A thin disc makes a lot of sparks if the tank walls are thicker .

Think Plastic , 2 tanks if one is hard to fit.

I have worked with these folks , a minor sketch or a visit will get the fill.drains in just the right spot.

There catalog is marked with which can travel UPS , a great cheap way to ship.

Fresh or Black water they make both.

DURACAST | ROTOMOLDING PLASTICS FOR THE FUTURE

duracast.com/
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Old 05-12-2015, 08:02 AM   #18
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If he offers you a glass of water ask for double Scotch in it!

How about using the tank for a fresh water anchor / deck washdown source?
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Old 05-12-2015, 08:24 AM   #19
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Quote:
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If he offers you a glass of water ask for double Scotch in it!

How about using the tank for a fresh water anchor / deck washdown source?
That, right there, is the only practical and safe way to use said tank for fresh water. Advise him modern food grade water tanks are great. I installed two 12 years ago, and (as Marin put it), the water tastes like water - no taint at all.
Even so I must admit we usually like to take insulated water containers with taps filled with filtered home water for actually drinking. The boats tank water is largely used for everything else. Ie washing up, showering, cooking, etc.

Please, please talk him out of that idea asap. That coming from a sanitation expert, (Peggy) and a quack, (moi), as well as everyone else on here.
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