Should I caulk the rubber gasket in my transitional coupling installed on a vertical ABS to Metal drain pipe? There is a slight seepage at the ends of the rubber gasket, and even though it might have been installed when the house was built in 1973 - the rubber feels like it's still tactile (not brittle, or hardened) so I'd like to avoid having to wrestle-on a new rubber gasket. If so, what type of caulk should I use?

Update: The leak isn't coming from the rubber gasket. It's coming from a hairline crack in the lower (inboard) edge of a collar on a 3-port ABS fitting mounted directly above the gasket. Now - I'm wondering why it would crack (it's inside an interior wall, where nothing can bump it).

It doesn't matter at this point why it is cracked, could be a flaw. You must replace the ABS fitting. Cut it out and install a new one using a hubless collar to marry it to he old ABS pipe.

I assume it is a drain fitting. Since they are not under pressure, you may be able to clean the crack, prime it and then use an ABS glue on top. If you are lucky, it may seal the crack or at least reduce it until you can replace it.

Do not use caulk. ABS is very easy to repair. When it comes to it, you can even use Fernco fittings to joint two ends of ABS pipe.

Milo

UPDATE: Thanks for the answers, everyone - problem solved. Yes - it is a drain line (laundry, kitchen), and I guess after 42 years of hot & cold water (heat expansion, contraction), the fitting developed a crack - and as it turn out, so did the fitting at the other end of the air vent ABS pipe that is connected to this same fitting. I learned something, in the process of taking care of this. Thanks!