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Author Topic: black water tank issue  (Read 2838 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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« 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

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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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« 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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« 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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« Reply #15 on: March 30, 2010, 12:38:28 PM »

Thanks for the replies. The tank had a split in one of the weld seams, which I tig welded to repair. The material is very thin so Im guessing there is another spot somewhere in the back weld. I was hoping for some kind of epoxy to put in the tank the seal all the welds. Since this is in the back 1/2 bay on my MC-7C not sure that plastic will give me much more than about 1/2 the size I have now(guessing about 75 gals now)
I will pull the tank again tonight (3rd times the charm I hope Grin) and try and pressure test it............
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73 MC-7combo
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« Reply #16 on: March 30, 2010, 01:10:06 PM »

Give up on that internal sealing stuff.  It has to be applied to a clean surface to work.

Van,

If you keep your tanks separate you can drain the grey into a ditch or ? thru a garden hose.  I can get withing 50 feet of just about any hole.  You can also do that with black but you need a macerate or really tiny poopies.

If you combine then the chems you use in dishwashing, etc, will "kill" the bugs that digest the black and it will emit odors outside that those down wind will find offensive.  My grey water really reeked but I let food scraps and coffee grounds into the grey.

You can only stack plastic if you put framing between them to support the load.  I wanted fresh on the bottom and grey and black on top.  Heating the fresh would also protect the other two from freezing.  I thought building mine from ABS or PVC black sheeting 3/8 would be the best ever.  I could install the baffles to be internal support to allow stacking without framing.  Fit to close tolerance and that watery solvent welds the pieces into a single piece.  You can fit joint reinforcement with the water solvent or use heavy body like the stuff they use in plumbing.  You could make any shape you want to fill any space.  The best I have seen use multiple tanks for fresh and grey all stacked and plumbed with nary a cubic inch to spare.  Lots of options. The black sheeting is reasonable but the white food grade is spendy.  I would plan to cook and drink bottled water if you made your fresh tank out of anything other than food grade.  Common flange fittings take care of connections. 
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« Reply #17 on: March 30, 2010, 04:08:54 PM »

Kyle is right, if you weld up a stainless steel tank, you HAVE to passivate it.  How many SS tanks have I seen that have not been passivated? MANY.  quite a few welding shops including some major SS tank manufacturers don't do it... and the result is always leaky welds and rusted out seams!

Fortunately there is a very simple (fairly new on the block) way to passivate.  First use a wire wheel to get the colors off that you've created during the welding, then use a "wand" and a tig welding supply, set at about 20 amps, and do it with this stuff: http://www.citrisurf.com/9002data.htm

Basically you create a "wand" by wrapping some scotchbrite along with a layer of fiberglass tape around the end of a piece of 3/8 stainless rod, hook the rod to the same terminal on your tig welder as your torch, ground the tank, set the welder at 10amps, dip the scotchbrite into a solution of citrisurf 9002, and wipe it slowly down the weld.
It'll create a giant sulphur stink cloud, but the job is almost instant and the electricity does the job. It eats the scotchbrite and fiberglass pretty fast.

Browse around the website http://www.citrisurf.com/  These guys have many passivation products based on citric acid that is very safe to use, environmentally friendly and most imporant, you can do it yourself.  I use the stuff daily and it's all like magic...
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« Reply #18 on: March 30, 2010, 06:41:31 PM »

There are different grades of SS.

Much to my surprise many years ago I discovered that a small magnet would stick to a supposedly SS kitchen vent??

If a magnet will stick it has iron in it, iron will rust. Simple but true.
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« Reply #19 on: March 30, 2010, 09:21:35 PM »

Actually most of it has some iron in it.  But it won't rust... that's what passivation is all about.  The main ingredients in common SS (304, 316 etc) are iron, nickel and chromium.  When the stuff is manufactured, any surface iron is removed by passivation and the resulting chrome on the surface oxidizes, creating a very robust non corrodable surface.  But when you weld, you re-alloy everything near the weld and some iron comes back to the surface...that's what rusts.  Removing it with citric acid or other means (passivation) re-establishes an iron-free surface and once again it won't rust or corrode.
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« Reply #20 on: March 31, 2010, 05:21:55 AM »

Well said Boogiethecat.

gus, all stainless steels, with the exception of the austenitic group (300 series), are strongly attracted to a magnet.
304SS can become magnetic if work hardened. It has to do with the atomic lattice straining and formation of martensite.

All stainless will corrode, it just corrodes slower than mild steel.
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« Reply #21 on: March 31, 2010, 05:49:07 AM »

The things you learn on a bus chatsite!  good info on welding stainless, I appreciate it.  I do it as little as possible, because I know that while I can run the bead just fine, I don't know how or have the equipment to do the second half of the job, the passivation.  Now I know a little more about what I don't know, and that's always good!

Brian
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« Reply #22 on: March 31, 2010, 08:12:12 PM »

Good things to know about SS. I assumed the purest SS had no Fe at all?

I do know that the SS screws I use on aircraft fairings can't be picked up with a magnet when I drop them into black holes!!

I've never seen corroded SS but have seen corrosion on other metals touching them and rust stains on the SS screws/bolts from plain steel.
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« Reply #23 on: March 31, 2010, 09:00:55 PM »

Gus,

I am with you on this.  The test, for me, and for those that advised me, was that SS was only slightly magnet.  Not enuf to pick it up.  And when I bought SS fabrications I specified "Marine Grade" SS along with the # of the stuff called out by the ME.  The stuff I had installed was on the coast within a couple hundred yards of the Pac.  It did not rust but did get a yellowish cast to it.  I, or rather the Merican Tax Payer, paid a princely sum for some of that stuff.  The aluminum stuff that I was always replacing and was specified and procured by Sperry became a white p[owder as did the framing of the semi we had out there.  Did you know that you can spec a semi trailer for operation in a high salt and corrosive environment?  That would have been thinking ahead, using same and this conversation has not taken a dive into sexual references or innuendo.

Really torn on this as The Boogie Meister is held in the highest regards in my household and I might seem to have taken up arms.  Be assured I haven't, Mein Heir.

I think you can make SS without using any nickel but the good stuff has a lot of copper content.  The next step up on the metal ladder is MONEL and they have two grades of that and the difference is nickel content.  I don't think it sticks to a magnet either.

No numbers or mil standards or even a USDA reference in my musings of 20+ years ago.

John
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« Reply #24 on: April 01, 2010, 06:42:24 AM »

I was involved with a textile machine that we used every grade of stainless available & they all corroded to failure within months of the install.
We had to use Inconel - seemed expensive at first, but it got cheaper the longer it lasted. Installed the Inconel over 15 years ago & it is still working great with no corrosion issues.

BTW, while Inconel has iron in it, Inconel 600 is usually slightly magnetic at room temperature, it will become non-magnetic when warmed mildly. Cold work or thermal treatment have little if any affect on its magnetic properties.


It is better to use 316L stainless steels when parts are to be welded. This is especially true if the weld may come in contact with chlorinated water. During welding, chrome-carbides are formed along the weld. This formation of chrome-carbides depletes the metal of chromium. Without the chromium, the protective passive film cannot form and corrosion can occur. This is called intergranular corrosion.

Damn, ain't nothing simple if you dig a little deeper. . . .  Roll Eyes
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« Reply #25 on: April 01, 2010, 12:51:45 PM »

Plastic is just looking better and better.  Of course, I am really old school and built plywood/fiberglass tanks.  As far as I know, they are still in the bus and working fine after twenty years.
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« Reply #26 on: April 01, 2010, 09:41:50 PM »

If done right, stainless tanks are fine. Just as plastic tanks.

Also, same as plastic, things will go bad if you don't do it properly.  Roll Eyes

FWIW, I've seen plenty of plastic tanks that leak too.  Shocked


A friend has a MCI-5 that was converted by custom coach from new (never a seated bus). His stainless tanks are around 50 years old & still no leaks.

And, yes, his bus is original, down to the 8V71 & 740 Allison that are still getting the job done.  Grin


My point is, before deciding on what to use - do your own homework to determine what is best suited for your needs. Cool

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