Black Tank Leak - questions

[wmcreid]

We have a 2003 Keystone Sprinter 5th wheel. The black holding tank had a repaired crack (8" long across bottom corner behind the valve). After approximately one year of use the repair began to drip and then pour. I plugged it with epoxy putty which lasted about a month, more epoxy - another month, and then a big gloopy gob of epoxy putty, gorilla glue, and space-age polymer ceramic that I found at a hardware store in Texas. After about a month the whole patch fell off into the dirt under my trailer and floated away in a river of yuck. We let the tank dry for nearly a month and I scraped and sanded everything along and around the area of the crack. I let it dry a couple of more days, sanded it some more and then I covered the whole corner area of the tank with loctite heavy duty epoxy resin and two layers of glass cloth. I let this dry for nearly a week. This patch worked perfectly. It was actually easier to accomplish than everything else I had done up to that point and I can honestly say that the epoxy and glass cloth is a sure cure if done properly. Unfortunately, two months after my sucessful repair I noticed liquid dripping from that area again. Once again we let the tank dry for a month and I climbed under there to inspect. The patch is solidly in place still and there are no apparent leaks anywhere around the tank. I've felt along the top of the tank flange where I can squeeze my fingers in, but I can detect nothing. The repair is solid, the tank is not leaking anywhere that I can see, and the drain lines and valve connections look good. I am at a loss here. I don't think it's possible to overflow one of things, and I think if that were the case there would be some indication visable, like the water rising in the toilet or something. Anybody got an idea here?

[EMD_DRIVER]

I had a severe black tank leak, on a travel trailer that we used to have. Instead of buying a kit, I went to Lowes and bought a can of ABS cement and a short piece of ABS pipe. I used a reciprocating saw to make several cuts along the piece of pipe. I gathered all the cuttings and put them in an old cup. I poured some of the ABS cement in with the trimmings and stirred it up. I had already cleaned the crack as best as I could and scuffed the area around it with a wire brush. I put a couple pairs of disposable gloves on and spread my weld in and along the crack. That was 5 years ago and that tank has not leaked since.

[geotex1]

Honestly, all the time and effort and materials put into repairing you could have replaced the tank. ABS is repaired by solvent welding a patch panel. Don't bother with anything else as it will not last because it won't fuse, just adhere for a time. However, aged and chemically contaminated ABS does not weld so well I would suggest as others and do a staged clean water test. If your patch is the culprit, consider a new tank.

[agesilaus]

I would certainly try that ABS repair kit before trying plastic welding. Here is a clickable link:

Amazon

[ed6713]

http://www.amazon.com/Plasti-Mend-Plastic-Repair-Holding-Tank/dp/B003JC3UB2/ref=sr_1_5?ie=UTF8&qid=1422580636&sr=8-5&keywords=rv+tank+repair+kit

Might try this.
EternaBond is also commonly used to repair waste tanks.

http://www.eternabond.com/AlumiBond-p/rv-as.htm

[NMDriver]

I guess you have filled the tank with clear water past the level of your repair and tried to find the leak. You can use red kool-aid or food dye in the water to help find the problem. Fill in stages and try using toilet tissue as a moisture indicator around your repair and other seams.

I suspect your repair is leaking, but I would be trying to figure out what structurally is wrong with the black tank support that is breaking the tank. There is no pressure in the tank so it is likely to be related to the weight of the tank and how it is supported.

I guess you have a plastic and not a fiberglass tank? If fiberglass then Kitty Hair should fix it for around $60 per can.

Good luck and although I have never used one, there are plastic welders out there.

[agesilaus]

I've heard here that you can find people who will "plastic weld" the crack for a permanent fix. Or you can buy the welder (Harbor Freight has them) and try the fix yourself.

Wiki


Harbor Freight Tool

As usual with HF: buyer beware.

And a Video:

YouTube