Converting a SS Grey Water tank to Drinking

Submitted: Tuesday, Nov 19, 2013 at 18:42
ThreadID: 105191 Views:1787 Replies:8 FollowUps:11
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Hi All,

In thread 105163 Twinkles asked about converting an aluminium fuel tank to a water tank.

My question is similar but different.

I have a 120 litre stainless tank with baffles that was a drinking water tank and has been re-plumbed and used as a grey water holding tank (due to the installation of another tank). I'm considering changing back again.

Do you think it is possible to clean it out? I have been thinking about strong chlorine to kill slime and scum, caustic soda to digest stuff so it can be flushed out, some kind of acid to have a go at what the other two can't deal with, and steam, but the baffles would get in the way of that.

Anyone got any ideas?

Thanks in advance

Frank
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Reply By: Iza B - Tuesday, Nov 19, 2013 at 19:05

Tuesday, Nov 19, 2013 at 19:05
I suggest a biological treatment first, left sit for several days to ensure all the food stuff is degraded. A serious chlorine treatment and lots of flushing should then get things back to safe drinking standard.

Iza
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Follow Up By: LIFE MEMBER-snailbait - Wednesday, Nov 27, 2013 at 17:47

Wednesday, Nov 27, 2013 at 17:47
hi
Use pool chlorine it is a bout 10 time better
Terry
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Reply By: Bob Y. - Qld - Tuesday, Nov 19, 2013 at 19:12

Tuesday, Nov 19, 2013 at 19:12
Frank,

Grey water leaves behind a lot of foamy residue, that would stick like you know what to a blanket. If you could get to it, it could be cleaned quite easily, but as that's not the case here, I'd suggest a diluted acid, to etch the interior, then followed by some sanitising, and deodorising. And as said above, lots of flushing.

But thanks all the same, I'll pass on that offer of a cup of tea, coffee, or a glass of water.

Bob.

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Reply By: Sand Man (SA) - Tuesday, Nov 19, 2013 at 21:21

Tuesday, Nov 19, 2013 at 21:21
Hi Frank,

I have just gone through a thorough cleaning of my camper 120l water tank.
I have been attempting to clean it on numerous occasions.
My problem was a persistent brown water contaminant that I just couldn't flush out in the normal way. I believe the tank may have been filled at some stage with muddy river water.

My final solution was to drop the tank so I could invert it in all directions.
I discovered this tank also had internal baffles.

Following a vigorous flush, I added a couple of cups full of household bleach, filled the tank fully and left it to stand overnight. (eg about 12 hours). The tank was left standing on one end, with the filler inlet and the drain and breather outlets uppermost.

I emptied the tank, filled it with clean water and emptied it again.

I again filled the tank, this time adding 1/2 packet of baking (bi-carb) soda to the water and again filled it. This was to neutralise the bleach taste.

Emptied it again and filled and flushed it again before re-installing it into the camper.
Filled it a final time and the water is now running clear and tastes normal.

I think the main problem with camper/caravan water tanks is the inability to completely flush it via the normal drain outlet, which is both small and not necessarily at the absolute bottom of the tank.
By being able to invert the tank after its removal, I could empty it completely via the larger filler inlet which was now at the absolute bottom. This allowed all deposits to be flushed out as much as the bleach could remove. The tank could be manually shaken about as the water (and therefore the weight) was reduced.

I would not recommend anything else but normal household bleach to use, after I did some considerable research on the web.
I used White King Regular bleach and two cups was a little more than was recommended for the 120 litre tank, but still within an acceptable limit.
Anything stronger could affect the stainless steel surface and seams and welds, etc.

I think the task is worth the effort, especially if, like my case, you can remove the tank.
It is not a simple job, but reassembly was assisted in my case by the use of a trolley jack to help locate the tank back into its recessed compartment.

Having only completed the job the weekend before last, I have yet to run the taps to check water quality for a final time but I am confident that I have been able to fully recondition the tank back to an acceptable water quality standard.



Bill


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Follow Up By: Member - Frank P (NSW) - Wednesday, Nov 20, 2013 at 14:57

Wednesday, Nov 20, 2013 at 14:57
Thanks Bill.

"Anything stronger [than bleach] could affect the stainless steel surface and seams and welds, etc."

I thought stainless was pretty impervious to most things like harsh cleaners, eg caustic soda, acids (both within reason of course - not too strong) Am I wrong?

I know there are different grades of stainless. I don't know what the tank is, but there are absolutely zero signs of rust or corrosion or discolouration on the outside - unlike my Chinese-made SS BBQ - so I'm reasonably confident that it is good material. External seams are rolled and welded, which I see as another indication of quality.

I just wish I hadn't been so rash in deciding to use it as a grey water tank. What a waste :-(

Cheers
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Follow Up By: Ron N - Wednesday, Nov 20, 2013 at 16:54

Wednesday, Nov 20, 2013 at 16:54
Frank - Stainless is not impervious to most things. Chromium, nickel and molybdenum are added to steel to make stainless steel, and the chrome content varies according to the stainless grade (304 stainless = 18% CR, 8% Ni - and 316 stainless = 16% Cr, 10% Ni and 2% Mo).

Chrome and nickel are dissolved by weak solutions of hydrochloric and sulphuric acid. When these acids are used to clean stainless, you can produce hexavalent chromium during the chemical reaction.
Hexavalent chromium is nasty stuff, it's carcinogenic, so you want to avoid it, at all costs.

Thus, if you use bleach initially, you get get rid of the bugs and the grease.
You then flush with water and clean out all the bleach/grease/bugs residue.
Then clean the tank with some citric acid, which then cleans any rusty spots or other alkaline chemical deposits - and citric acid will also assist in neutralising remnant bleach.
Then flush the tank again with clean water and add a moderate strength solution of sodium bicarbonate, which will neutralise any acidity left by the citric acid, and also "oxygenate" the tank, as sodium bicarbonate is a strong oxidising chemical, and an excellent health tonic in the body as well.
Sodium bicarbonate is used medically to remove many toxins from the human body, and you can't harm yourself with it.

Cheers, Ron.
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Follow Up By: The Original JohnR (Vic) - Wednesday, Nov 20, 2013 at 21:35

Wednesday, Nov 20, 2013 at 21:35
Ron, interesting what you are saying about using weak acid solutions against stainless finishes. It makes me think that the items of stainless in our dairy plant would have been made porous years ago. Used plenty of quite concentrated acids, including the ones you quote, nitric too and phosphoric acid at high concentrations. Talking 304 grade here though. I don't think that moderate concentrations for the few minutes of cleaning would trouble 304 or 316 grades would worry the stainless tank.

Rusty spots are common in stainless welds and in some walls, but we found best polished. In the tank Frank is talking about, the visibility I expect it not to be an issue. Stainless is the front one isn't it Frank? Are you taking it off to clean it out?

With the dairy plant it was always suggested not to have the water too hot with the newer chemicals. 70° C is good to avoid cooking on the fats, but you do want to be able to flush it out after. Not always easy to get that with modern HWS systems!

Cheers,
Who?
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Follow Up By: Member - Frank P (NSW) - Wednesday, Nov 20, 2013 at 21:48

Wednesday, Nov 20, 2013 at 21:48
Hi John,

Yes, it's the front one. I had the 120 litre rear plastic tank installed and decided to retain the front one, re-plumbed as a grey water tank. Now thinking about restoring it to drinking water standard and installing the Group's grey water tank in the A frame.

I will be removing it for agitation and easier inspection.

Cheers

Frank
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Follow Up By: Ron N - Wednesday, Nov 20, 2013 at 22:12

Wednesday, Nov 20, 2013 at 22:12
JohnR - No, you're right, short periods of acid contact aren't going to worry the stainless steel too much.
I was just concerned about the creation of by-products from the acid treatment that could be hazardous.

Surprisingly, in many instances, a weak acid will etch a metal faster than a strong acid. The characteristics of acids change with strength levels. Strong acids can actually be oxidising agents, against all initial thoughts.

Here's a webpage about stainless steel descaling and pickling (cleaning) after fabrication. The article is quite extensive, and goes right through to consumer care and cleaning of stainless steel, offering a wide range of stainless cleaning options.
Sodium tri-phoshate rates a mention, it's the common constituent of laundry powder. Oxalic and phosphoric acid also come in for mentions, but each chemical provides a solution for different problems.

Cleaning and Descaling Stainless Steel

Cheers, Ron.
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Reply By: The Bantam - Tuesday, Nov 19, 2013 at 21:36

Tuesday, Nov 19, 2013 at 21:36
A multi stage atack is probably best in conjuction with a road blessed with a lot of traffic calming.

I recon napi san..lots of it.... would be a good starter.......its pretty usefull and inocuous....... and is designed to shift greasy slimy stuff.

a couple of slow laps over a series of speed bumps.....preferably diagonally.

Citric acid is a pretty good cleaner and is used for everything from cleaning roofs to sterelising medical equipment.....one of its big advantages is it rinses out cleanly.

cheers

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Follow Up By: Member - Frank P (NSW) - Wednesday, Nov 20, 2013 at 15:03

Wednesday, Nov 20, 2013 at 15:03
G'day Bantam,

I use generic NapiSan as a routine additive to help control smells coming up the shower and sink wastes - neither have proper P traps.

Point taken about crossing speed bumps diagonally. No shortage of those around here, though I think I will take Ron's suggestion below and remove the tank and tie it to a concrete mixer for agitation.

Yes, for the acid component of the process I was thinking of citric.

Thanks for your reply.

Cheers
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Follow Up By: Member - Frank P (NSW) - Wednesday, Nov 20, 2013 at 15:05

Wednesday, Nov 20, 2013 at 15:05
"I use generic NapiSan as a routine additive to help control smells coming up the shower and sink wastes - neither have proper P traps.
"
Should have added ..

- so hopefully that will have controlled the buildup of grunge somewhat.
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Reply By: Member - KeithB - Tuesday, Nov 19, 2013 at 22:19

Tuesday, Nov 19, 2013 at 22:19
I think you are on the right track.
With grey water, there might be a lot of body fats stuck to the insides of the tank.
I'd start with some caustic soda to eat out the fatty sludge. Then rinse and go with bleach and rinse with water and a little dilute acid to take out any left over caustic soda.
You'll either be left with a clean tank or no tank!
Whitworths sells a nice Stainless waterproof hatch that you might be able to hole saw into place. That might give you better access.
Stainess deck port
You might have to put a couple of blobs of Sikafles on it to stop it unscrewing. I'll be using them in my tanks.
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Reply By: Ron N - Wednesday, Nov 20, 2013 at 11:26

Wednesday, Nov 20, 2013 at 11:26
Frank - Use only bleach and citric acid for cleaning (separately, of course), and only sodium bicarbonate for neutralising.
Tank removal is the only sure way of getting all the crap out.
If it's possible, after putting a few litres of your cleaner in the tank, strap it or clamp it firmly to a rotating item - a tractor wheel, a concrete mixer, or something similar.
This is the method we use to clean rusty fuel tanks when doing restoration work. It works very well.

Cheers, Ron.
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Follow Up By: Member - Frank P (NSW) - Wednesday, Nov 20, 2013 at 14:46

Wednesday, Nov 20, 2013 at 14:46
Thanks Ron. I never thought of attaching it to a concrete mixer. I was worried about agitation and you have solved that one for me.

You seem pretty definite about only using citric acid and sodium bicarbonate for cleaning. Any reason for that?

I was thinking that because the tank is stainless I could use more aggressive stuff first to deal with slime and solids. Then wash and rinse with gentler "organic" cleaners, followed with a thotough flush with water.

Cheers
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Follow Up By: Ron N - Wednesday, Nov 20, 2013 at 16:29

Wednesday, Nov 20, 2013 at 16:29
Frank, the reason I suggested those three items, is because bleach is a confirmed bug-killer, and one of the most effective degreasers you can use.

Citric acid is "food safe" (you can eat it, it's a regular food additive and preservative), and it's one of the best and safest metal cleaners around - and sodium bi-carbonate is also "food safe", and is one of the best acid neutralisers you can get.

Cheers, Ron.
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Reply By: Member - Frank P (NSW) - Wednesday, Nov 20, 2013 at 15:13

Wednesday, Nov 20, 2013 at 15:13
Thanks everyone for your replies, I think I have a handle on it now.

If I were to use bleach, caustic soda solution, citric acid and bicarb soda as a neutraliser, what do you think would be the best order. (I understand the need to neutralise between caustic soda and the acid and vice versa)

Wish I had a tractor (Thanks for the idea, Ron), but not much use for one of those in suburbia. A hired concrete mixer will have to do.

Cheers
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Follow Up By: Ron N - Wednesday, Nov 20, 2013 at 17:03

Wednesday, Nov 20, 2013 at 17:03
Frank - If you use bleach, you won't need to use caustic soda - and you may even be able to eliminate the use of citric acid, and just use bleach and sodium bicarbonate. It all depends on how good the tank looks once you've used the bleach.

Make sure you flush the bleach from the tank before you use citric acid, as adding citric acid to any modest quantity of bleach, produces serious amounts of chlorine gas, and you don't want to be breathing that.

A small amount of chlorine gas is O.K., but bleach produces chlorine gas as it breaks down anyway, that's what kills the bugs. So don't breathe the bleach fumes too heavily, either.

Cheers, Ron.
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Reply By: kev.h - Wednesday, Nov 20, 2013 at 21:47

Wednesday, Nov 20, 2013 at 21:47
Try one of the citrus cleaners ie. Citra clean that will strip any fat or grease from the tank
We use it at 3 times the label rate as a grease remover works a treat
Kev
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