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Old 12-13-2008, 06:59 PM   #1
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Cracked Black Water Tank Invert Repair

The invert on my black water tank is cracked as shown. The tank otherwise seems in very good condition. Would like to avoid having to buy a new one due to cost but realize it might be the best thing given the hassle of removing these tanks let alone remounting (haven't tried putting one back on yet).

Any ideas on how this might be fixed? I am thinking of making a patch for the outside using polyethlene sheet or pipe, caulking the patch and outside of the invert and clamping the patch on with band clamps; also replacing the Thetford flange mount that fits into the invert by "glueing" it in using caulking. You can see the crack on the inside on the thetford flange picture (sorry about the inside shot!)

Has any one used Vulkem as adhesive and caulking to try and help water proof such repairs, and if so has it held? What about radiator sealer/hole plug repair kit?
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Old 12-13-2008, 07:06 PM   #2
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Quote:
Originally Posted by toga View Post
The invert on my black water tank is cracked as shown. The tank otherwise seems in very good condition. Would like to avoid having to buy a new one due to cost but realize it might be the best thing given the hassle of removing these tanks let alone remounting (haven't tried putting one back on yet).

Any ideas on how this might be fixed? I am thinking of making a patch for the outside using polyethlene sheet or pipe, caulking the patch and outside of the invert and clamping the patch on with band clamps; also replacing the Thetford flange mount that fits into the invert by "glueing" it in using caulking. You can see the crack on the inside on the thetford flange picture (sorry about the inside shot!)

Has any one used Vulkem as adhesive and caulking to try and help water proof such repairs, and if so has it held? What about radiator sealer/hole plug repair kit?
Plastic welding may work. JB Weld may hold for a while as well. You best bet is a new tank. If you decide to go the fisrt route all surfaces needs to be very clean for the adhesive to work.
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Old 12-13-2008, 09:19 PM   #3
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Quote:
Originally Posted by toga View Post
The invert on my black water tank is cracked as shown. The tank otherwise seems in very good condition. Would like to avoid having to buy a new one due to cost but realize it might be the best thing given the hassle of removing these tanks let alone remounting (haven't tried putting one back on yet).

Any ideas on how this might be fixed? I am thinking of making a patch for the outside using polyethlene sheet or pipe, caulking the patch and outside of the invert and clamping the patch on with band clamps; also replacing the Thetford flange mount that fits into the invert by "glueing" it in using caulking. You can see the crack on the inside on the thetford flange picture (sorry about the inside shot!)

Has any one used Vulkem as adhesive and caulking to try and help water proof such repairs, and if so has it held? What about radiator sealer/hole plug repair kit?
The tank will continue to crack because of the aged material.

You can repair it, but the same thing will occur in the same places as well as others.

Andy
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Old 12-14-2008, 09:04 AM   #4
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Leakage

There is a specific product just for repairing polypropylene material. You can find it at larger RV stores. I repaired a black tank in 2003 and it has still held.

Your mileage my vary

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Old 12-15-2008, 08:22 PM   #5
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Thanks for the info - not sure wheter I will try and fix or order new tank. Am looking into some scotch weld 8005 for a possible try but will also will look into ordering new tank.
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Old 03-25-2009, 09:35 AM   #6
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I had a cracked polyethylene holding tank on a boat which I successfully repaired using Marine Tex FlexSet and flame treating the surface so that it would adhere a patch. I wanted to use the 3M Weld but the cost of buying the adhesive plus the applicator plus the tips, etc. in non commercial quantities was just too high for me. As it worked out the Marine Tex did the job within my price bracket. Be sure to get a piece of patch material to scab on which is as close to the tank material as possible. If the tank is polypropylene this won't work.

I also agree with Andy that the poly has lost it's plasticizer components and become brittle and you're likely to develop new cracks in other places.
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