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Author Topic: black water tank issue  (Read 2721 times)
txjeff
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« on: March 29, 2010, 07:06:20 PM »

i have pulled the SS tank out of compartment and welded seam that was leaking.  Also, reinforced the seam with JB weld and piece of aluminum angle.  Put water to test and did not leak.  After installing the SS tank, filled it 1/4 with water, while hooking the connections.  After about an hour, the repair started leaking .ARRRRRRRRRRR!!!!!    My question is............  is there any type of sealant that can  be poured into the tank to seal the seam from the inside.  One issue I have - there is baffel in the tank to prohibit reaching the area that is leaking by hand.  Any suggestions, comments, thoughts  - HELP?Huh 
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73 MC-7combo
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« Reply #1 on: March 29, 2010, 09:58:57 PM »

  There may be another leak. I had a similar problem with a fresh water tank. I wouldn't leak till I installed it. I wound up putting it on the bench and adding 5 lbs of air pressure to it. Then I did the soapy water in a spray bottle till I found all the pin holes. 5 I think. All within a couple of feet of the original patch...Cable
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« Reply #2 on: March 30, 2010, 04:18:14 AM »

You can waste a lot of time trying to fix and never get it right and risk the chance of it failing when on the road or buy a new one and get over with it.
Try www.Plastic-Mart.com they have hundreds of tanks in many sizes, find one and that is close and they will put the fitting any where you want. I bought my 110 gallon tanks from them. I went with the Marine tanks which are 3/8 of and inch thick. They have a build sheet that can be printed out, mark the locations and fax back and they will call you with pricing etc. Good Luck.
« Last Edit: March 30, 2010, 09:30:39 AM by scanzel » Logged

Steve Canzellarini
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« Reply #3 on: March 30, 2010, 05:18:07 AM »

Forget the JB. Weld it up right and it should hold. Cable is probally right, look for another leak. Good luck.  Tom Y
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Tom Yaegle
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« Reply #4 on: March 30, 2010, 06:08:39 AM »

Personally I would replace it/them. Possible fix might be motorcycle tank sealer. (Prolly nearly as expensive as replacement). You would have to be able to rotate the tank to distribute/deposit the sealer where needed. I'm unsure what that might do to the "bug" population of a waste tank. DO NOT try this with a fresh water tank.

Don & Sheila
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kyle4501
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« Reply #5 on: March 30, 2010, 07:30:42 AM »

I'd clean the tank down to clean stainless.
Pressurize tank with 5 psi air.
Use soapy water to locate all leaks & mark their location.
If necessary, cut in an access hole in top to survey the interior to determine the extent of the damage.

If a repair is feasible, weld up tank with the proper filler metal to ensure the welding process doesn't create new cracks. Might be prudent to find a local fab shop experienced in welding stainless have a look at it - one of their welders may be interested in a 'side job'.

Stainless steel tanks can suffer from corrosion, passivation is an important step to reduce it.

http://www.iftworldwide.com/white_paper/passivation.pdf  explains passivation in more detail for those with inquiring minds. . .  Grin
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« Reply #6 on: March 30, 2010, 08:28:46 AM »

When I was driving truck cross country, I had a full apartment behind my cabover in a 8ft square cargo box (shower, toilet, sink, microwave, refer, bed, etc).  With the limited space, I installed a 20gal black tank (enough for a week), and a 25 gal black tank (about 3-4 days use) between my lower fuel tank cross supports and the drive shaft on plywood platforms with angle iron reinforcements.  In the 705,000 miles I drove the truck, only had to replace the black tank once from an exhaust leak that melted it.  The 25 gal gray tank was original when I removed them to make the truck into a motorhome.  I used El Monte Plastics (who makes their own tanks) and would suggest you change to the plastic tanks also.  Nice thing about the plastic tanks is that you can weld with a propane torch with another plastic rod to repair them in place (but for me that never happened).  I am using a 175 gal water tank, 110 gray tank and 65 gal black tank in my truck.  Good Luck, TomC
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« Reply #7 on: March 30, 2010, 08:47:25 AM »

I'm going to use stainless steel tanks. I will have them fit the space exactly as I need. I'm also planning on having them vertical vs. flat. For my plans, this will maximize space utilization. Not as expensive as many make out - IF you cultivate a relationship with an industrial sheet metal fab shop that works with stainless. If you let them use your project as 'filler' work during slow times, you may get a better price.

In my plan, the formed plastic tanks don't allow as much flexibility & don't leave enough open bay space. (I may have tall bays, but I only have 2 of them.)

For txjeff's case, replacing the existing tank will likely require tons of work to re-plumb everything & loose tank capacity since the plastic tank will likely be smaller in 1 or 2 directions. However, properly repairing his existing tank (even if it requires a new bottom) will likely cost less time & money in the long run.
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« Reply #8 on: March 30, 2010, 08:52:10 AM »

Kyle- all of the plastic tanks I've looked at are made to be used in any position-meaning you could stand them up tall.  Also-you could stack your tanks.  You could install the black tank on the bottom with the gray tank above-then you could plumb the gray tank into the black to rinse it when draining.  Believe me-plastic tanks are SO much easier.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #9 on: March 30, 2010, 09:09:32 AM »

anyone have any recommendations where to get stack able tanks? I sure would like to hear the pro's and con's on using a combined Gray/Back tank vs the separate tank for each install. Getting ever so closer to this stage, best I start inquiring now, thanks.V
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« Reply #10 on: March 30, 2010, 09:34:23 AM »

Kyle- all of the plastic tanks I've looked at are made to be used in any position-meaning you could stand them up tall.  Also-you could stack your tanks.  You could install the black tank on the bottom with the gray tank above-then you could plumb the gray tank into the black to rinse it when draining.  Believe me-plastic tanks are SO much easier.  Good Luck, TomC
I have everything I need to work with the stainless. If I were to use plastic, I'd have to either farm it out or buy more tools & learn the technique -SO- not easier for me.

I'm not suggesting stainless is always better. One needs to look at his or her own application & choose what will work best.

BTW, I have used both plastic & stainless tanks in the past. I like the stainless better for my needs & desires on my bus. I am building this bus for me. If the next owner wants something different, he should have paid me more now.
I have looked at the available plastic tanks - to use a size or shape that that is available would not allow me to do what I desire.
For a given exterior size, including proper support, the ss tank will hold more water. You may not think that little bit matters now, but your opinion may change if you need just one more flush before you can dump.  Shocked
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« Reply #11 on: March 30, 2010, 09:45:52 AM »

I've heard of stainless tanks corroding numerous times.  It does seem that plastic will outlast them.  In Jeff's case, one can assume that if it is eaten through in one place, it is about to start leaking in several others.  He could possible cut a nice opening in the top and coat or fiberglass the inside.  I wonder if one could just completely re-line the tank from the outside like welding new stainless sheets to sides and bottom.
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kyle4501
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« Reply #12 on: March 30, 2010, 09:48:32 AM »

anyone have any recommendations where to get stack able tanks? I sure would like to hear the pro's and con's on using a combined Gray/Back tank vs the separate tank for each install. Getting ever so closer to this stage, best I start inquiring now, thanks.V
I have 30 gal black & 30 gal grey in my Airstream. The grey fills up much faster than the black.

For the bus, I will have a 30 gal black under the toilet (toilet is over the drive axle) that will dump via a slide valve into the main tank which will be a combined black & grey tank. My initial plans are for between 200 & 300 gallons of waste capacity. This will allow more flexibility in using the bus & how often we have to stop for 'proper facilities'. The goal is 2 weeks between having to dump with 4 of us on board. This will allow more options for where we can park if no set up is needed.  Grin

I have a friend who made a 500 gal waste tank for his father in law. They frequently use their bus & like not having to dump until they get home.

At 8.34 # per gallon, the weight adds up, but I have no worries about my 4501's ability to handle the 2500 pounds.
If it is a concern, I can always dump earlier.

You can dump your tanks any time you are at proper facilities, but, if your tanks are full, you can't add more to them . . . .  Shocked
« Last Edit: March 30, 2010, 12:46:05 PM by kyle4501 » Logged

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kyle4501
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« Reply #13 on: March 30, 2010, 09:56:21 AM »

I've heard of stainless tanks corroding numerous times.  It does seem that plastic will outlast them.  In Jeff's case, one can assume that if it is eaten through in one place, it is about to start leaking in several others.  He could possible cut a nice opening in the top and coat or fiberglass the inside.  I wonder if one could just completely re-line the tank from the outside like welding new stainless sheets to sides and bottom.
Yes, stainless corrodes. that is why I posted the link describing the passivation process & why it is an important step in the process of building a ss tank.

Instead of cladding the tank, I'd cut the top off & have a new bottom made - think shoe box - then I'd either weld the top on, or (if I felt it necessary to access the interior later,) I'd bolt it on.

Once you learn the idiosyncrasies of welding stainless, it is no more difficult than working with mild steel.
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« Reply #14 on: March 30, 2010, 10:32:02 AM »

TXJEFF didn't say how he welded the tank, but stainless is notorious for creating big oxides on the reverse of the weld if you don't back purge the weld with welding gas, and the oxides can create porosity and leaks.  I Tig weld stainless, and back purge with argon, and while the actual welding is dead simple - stainless is actually about the easiest metal to weld I have ever found - the back purging and the equipment to do that, and the total waste of argon makes me charge double when I do agree to do it...

Brian
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