Drip

I used JB Water weld to fix a cracked fitting on black tank. this stuff is made to fix water leaks and will even work under water

FWIW, I had a grey tank drip a couple of TTs ago.

Then one day I bonked the dump pipe on some dirt and grass in an awkward back up parking job. Leaked worse after that.

I took it apart to fix it and the black ABS pipe was only thrust into the fitting. The boneheads at the factory neglected to glue the pipe in place.

Easy fix, pull it apart, clean up the area, some ABS glue, done!

If it happened to me, it can happen to anyone.

Dutch has an excellent idea.

For black ABS "Plasti-Mend" will provide a permanent fix in all positions.

Buy direct from website or amazon.

If I don't have repair tape handy for a low pressure leak, I've also had good luck using Eternabond on dry pipe. If the area is exposed to weather or road hazards, a couple of layers of Gorilla tape or similar over the Eternabond will provide protection. If it's a coupling or worn spot that's leaking, a Fernco rubber coupling can be used as a permanent fix.

Fernco 1-1/2"x1-1/2" Flexible Coupling

flex tape as a temporary fix.

Definitely sooner...not later. Leaks don’t improve and a black leak is nasty.

Some of that self stick silicone repair tape will do a temp repair:

Repair tapes

You need to stretch the tape and pull it as tight as you can to get it to work.

Your local hardware will carry one or the other. You need to do a permanent repair sooner of later.