On Sat, 6 Sep 2014 09:43:51 -0700 (PDT), trader_4
wrote:

On Saturday, September 6, 2014 12:36:13 PM UTC-4, wrote:
It would help to tell us what kind of pipe, plastic/metal, diameter, etc!!!

If it uses a nut, they typically have plastic seals. New? Old?
Many times when they leak it's because the pipes aren't aligned
straight. Pipes need to line up, you can't rely on the fitting to
pull together pipes that are off on a slight angle. Also, you want
them to be hand tight, maybe a little more, as a starting point. If
it leaks, you can tighten a little more, but they aren't intended to
be made up real tight and oftern leak more if they are overtightened.

OP doesn't mention a garbage disposal. I'm thinking vibration on the
drain pipe.