need to patch my black water holding tank

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xcaret

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My rv is a 1980 model,and has a black holding tank for the sewage. I backed up into a rock and it pushed the strap holding the tank ,and part of the tank back,and a now theres a tear in the tank where it buckeled . I droped one end of one of the straps holding the tank and the tank just stays buckled.
I asked the rv dealer if they had anything and they asked if the tank wall was 1/4 of and inch thick or closer to 1/8 well its closer to 1/8 and plastic kinda stuff . They said they had nothing for it. Im thinking of getting a tube of pl 400,or whatever pl adhesive is flexible when dry,and after checking that it sticks to the tank , I'm gonna fill the tear with pl and let it set up, ozing out and around the hole , both on the inside and outside of the tank. I'm hoping it remains flexible and works like stuffing a rag in a tear.
.
Any ideas?
 
That probably will not work. there is a thread titled "holding tank issues" in the trailer and 5th wheel forum dealing with this very thing now. That is ABS plastic and very few things will stick to it other than ABS glue. The OP of that thread found some tank repair product that he is going to use and I myself think that fiberglass and resin would work. Good luck with your repair, perhaps a picture would give a better idea of the size of your repair for better answers. The motion of all that waste sloshing around will create a lot of force so any repair will have to be quite sturdy.
 
Go buy you a new tank. I have tried everything for friends, and when I had a boat tried to repair using many different techniques, my suggestion is save your labor and install it one time with a new one.
 
Somebody posted this earlier - said it really worked well.

http://www.amazon.com/gp/aw/d/B003JC3UB2/ref=redir_mdp_mobile
 
First thing to do is locate the ends of the crack and drill a hole at each end to keep the crack from spreading.  1/8" to 1/4" is fine - the main point is to be sure the rounded edge of the hole extends beyond the crack and into unbroken plastic.

The other thread on repairing holding tanks is here.  I like Marc's suggestion of mixing ABS shavings with ABS glue to make a putty to fill the crack.  Maybe even lay down a piece of fiberglass mesh over the crack once you're done filling it and work some thin glue/ABS putty through the mesh like you'd apply epoxy to help hold both sides together.


 
I've seen this trick for ABS but never tried it: Mix some Styrofoam shavings (e.g. from a disposable coffee cup) with ABS cement to make a thick paste and use it as a patch. Supposedly used by construction guys when they accidentally drill or saw into an ABS pipe.  However, there are commercially made ABS patching compounds on the market - might be safer to use those.

But the tank in this case may be polyethylene rather than ABS. That's much harder to fix.  Even epoxy resins don't stick well to poly.  I see where some people have had success melting another piece of poly and forcing it into the gap. Probably works ok on cracks but maybe not so good on gaping holes? There are some polyethylene repair kits on the market, mostly for canoes & kayaks, but they involve a welding-like process. Here's one:
http://www.plentypupule.com/weldkit.htm
 
You can almost repair anything. But the question is, will it last. On a black tank that holds human waste I would never gamble on a cheap fix from a little you tube patch kit. I have tried using nylon repair patch w/ epoxy, I have tried using mat and fiberglass and I have tried using a weld technique using the proper welding materials to try to get a perfect marriage. Well there's not one. I guess if you could get to both sides of the damaged area you could have somewhat of success. but most of your repairs are going to be from the outside only and that's like putting a bandaid on a gash that needs stitches. I just finished  repairing a fan shroud to a classic that the owner says there is not one in the country to be had and it turned out great. I took a cutter and trimmed a piece from the bottom and used it as my welding rod. I melted it in using a soldering gun with a paddle tip and it turned out great, but I was able to do both sides. If I was only able to access one side it would not have been a successful repair. Good luck...
 
If the spot is accessible and small enough, use a marine inspection deck plate to seal it. Pre drill the screw holes, goop everything up with some 3M 5200 screw it down.
One of these.
http://www.attwoodmarine.com/store/product/Deck-Plate/Inspection-Port

Bill
 
I fixed my grey water tank with ABS glue and some ABS plastic and fiberglass screen.  It seemed to fix the cracks but it still has a small drip.  Is there something I can put in the tank to seal the hole(s) I can not see?

Travis
 
I once patched a TT waste tank temporarily by drilling the ends of the crack as said, and sanding around the area to make sure it was as clean as possible. Then I patched the crack with a piece of Eternabond tape backed up by a piece of 1/8" aluminum plate held in place with several self taping screws sealed with silicone sealer. When I asked the owner several years later what the permanent fix was, he told me my patch was still holding and he hadn't done anything else about it.
 
If it's not ABS  it's probably poly.  Polyethylene can be welded.  Back when sailboard were rotomolded poly-whales we 'welded' them all the time because they had a habit of splitting along the rails.

The tough question is - does anyone still do polyethylene welding?  Try a place that sells or repairs kayaks.
 
Small hole. I would find some of the same plastic and coat it with GOOP , then lay it over the hole and drill either 4 or 8 SMALL holes and fill 'em with Goop covered stainless steel screws.

In fact that is now i installed the tank rinser device some 12 years ago and it's still holding.

Larger holes.. Well perhaps larger plastic.
 
You might try a fuel tank repair kit or sealer. The kits are for fixig larger cracks, but if you only have a seepage you can probably get by with a sealer/caulk designed for wet locations.

Permatex makes a plastic tank repair kit.
https://www.permatex.com/products/specialized-maintenance-repair/radiator-tank-repair/permatex-plastic-tank-repair-kit/

YouTube has several videos on repairs for polyethylene (poly) tanks. Here is one of them:
https://www.youtube.com/watch?v=u829qLroshw
 
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