Black water tank leak at the drain fitting - 2307C

oldcarguy

oldcarguy

Senior Member
Joined
Mar 10, 2018
Messages
170
Location
Sacramento CA
Have very recently developed a leak at the fitting where the plumbing from the drain valve manifold connects to the bottom of the black tank. Best as I can tell, the fitting that the manifold pipe is glued into has lost its seal to the body of the tank, probably due to the drain valve manifold bouncing around due to the uneven and broken pavement of our crummy roads.

Did a search on this forum, found one thread dealing with making repairs to this fitting from about 8-9 years ago. At that time the recommendation was to build up layers of ABS glue and fiberglass cloth over the leaking area to seal it - has anyone had recent experience with making this repair? Any suggestions for updates to the repair procedure and/or newer more effective materials? I'd really prefer not to have to replace the entire tank if at all possible....
 
Black Tank leak

DH had to do this repair on our 1990 25FT. Classic. DH did the repair as you have posted. Look on You Tube for advice. Check the net for RV repair kits. You shouldn't have to replace your entire tank. Best of luck with this repair.
 
I did this repair with abs glue and Fiberglass mats a number of years ago and it still holding
The trick is to do a number of layers while each layer is still wet ( I think I did 4 layers)
I also added a 16 gauge strap to the black tank pipe
Which I attached it to the frame of the trailer and added a spacer at that point so there is no more pipe flex at the black tank
 
I also repaired this leak this way and it has held up fine, for several years now. Do it! It works and is not a difficult thing to do.

- Jack
 
Same here, I fallowed JackandJanet instructions about 2 Years ago. Had no problems since. RV repair wanted $ 2000 to replace the tank. Good Luck
 
Thanks for the responses - I've done quite a bit of ABS and other plastics fabrication over the years, so hopefully this shouldn't be a big issue to resolve.

Fabricated a small bracket to stop the manifold bouncing around yesterday - bracket bolts to the two lower mounting flange bolts on the black tank valve and to the valve guard strap that runs parallel to the frame rail under the valves. It's a simple little bracket cut from a piece of scrap sheet (about 10-12 gauge) and should completely immobilize the manifold. Photos of the bracket attached - first three are of the bracket installed to trial fit before final trimming and painting, last one is painted before final install.

The pipe run to the gray tank is quite a bit longer than the run to the black tank - considering fabricating a second bracket to insure that section is immobilized as well.
 

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Last edited:
oldcarguy said:
Thanks for the responses - I've done quite a bit of ABS and other plastics fabrication over the years, so hopefully this shouldn't be a big issue to resolve.

Fabricated a small bracket to stop the manifold bouncing around yesterday - bracket bolts to the two lower mounting flange bolts on the black tank valve and to the valve guard strap that runs parallel to the frame rail under the valves. It's a simple little bracket cut from a piece of scrap sheet (about 10-12 gauge) and should completely immobilize the manifold. Photos of the bracket attached - first three are of the bracket installed to trial fit before final trimming and painting, last one is painted before final install.

The pipe run to the gray tank is quite a bit longer than the run to the black tank - considering fabricating a second bracket to insure that section is immobilized as well.
Click to expand...

Nice work 🔩
 
I tried to patch it per suggestions and it still leaked. I ended up putting in a new tank. I think the real issue is the stress on joints and the fact the plastic gets brittle and thus cracks. I used flexible coupling plumbers use to connect ABS when things don't exactly lineup. So the tanks, including grey water, are isolated from the outlets as well as each other.
 
Completed the repair on the black tank drain line a few days ago - 3 layers of black ABS cement (1st layer thinned with TAP Plastic's water-thin solvent acrylic cement so the ABS cement would penetrate better into any existing cracks and/or seams) with layers of fiberglass cloth in between. After curing overnight, filled the tank 2/3 full and let it sit for 24 hours, no visible leakage. Only time and travel will tell whether the repair will hold up.

Added a second rigid support to the smaller pipe running from the valve manifold forward to the gray tank - just a simple piece of flat sheet stock that bolts to the adjacent frame cross-member and loops around the pipe.
 
Oldcar - I suspect your repair will last as long as you own the trailer. The ABS fiberglass patches along with your brackets will have plugged the leaks and eliminated any flexing, which is what causes the leaks in the first place.

- Jack
 
if it keeps a boat afloat....

I had a very small leak at that joint, a seeping leak. I decided to try Flex-Seal to stop the drip. If flex-seal can turn a screen door into the bottom of a boat, I figured it just might work. I used the spray version and alternated thin coats of white and black for 10 layers. Alternating colors allows one to see how well the new coat is covering the older one. So far no problems.
 
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