Leaking Black Tank Pipe

use abs cement its made for that pipe ands its what trades use...

If it has a u joint tighten the nut or if it's a direct fitting use some PVC cement and be careful it will set up fast so have it where you want it.

The pipe is ABS. Personally, I would use ABS cement for the repair. Without a photo, it is difficult to advise you on a method.

If it is leaking a the way around the coupling, I would get another coupling, cut about 1/4" off the bell. I would split the 1/4" bell ring. Wipe the existing ABS coupling with a dry rag, no need for special cleaning. put a liberal coat of the ABS cement around the joint of the existing bell/pipe. put the two ring pieces on the pipe, up against the existing bell. Apply another coating of cement. You can apply several coats of cement. It is optional to wrap a piece masking tape around the cemented joint, but it will definitely take longer to cure.

I have experimented with ABS pipe, in my garage. I have cemented two pieces together, and cut them in half. I even polishes the cut to see if the two pieces were actually fused together. I could see no sign of a crack. I have even split a couple of 8-inch lengths of 3-inch ABS pipe, heated them and made them flat. I cemented them together with the ABS cement. I could not separate the pieces with a hammer and chisel. The only cleaning I did was wipe off the pieces with a rag.

Many of today's automobiles use ABS in many places. I have also used the ABS cement as a filler and to fix cracks on a damaged automobile grill.

Wayne

Drain and clean as best you can, then park the rig so the bad joint is higher than the pipes coming up to it. Clean, clean, clean.. all around the bad spot.. right down to alcohol or something that dries clean and scrubbed..

Then put it on.. and you will succeed. I did the same with a white water line and epoxied the joint and it held forever.

+1 on JB

Plasti-Mend is a bit pricy but I guaranty it would be a permanent fix.
Find it on amazon

I would use jb weld

Here is what I have used on a water line, still holding up.

Silicone self fusing tape

Or

Silicone Tape

Good Luck