On Jan 24, 7:34*pm, wrote:
On Jan 24, 1:10*pm, Limp Arbor wrote:

Probably the old nut you took off had a built-in washer. *I too have
copper drains and the nut that goes on the end has a thin piece built-
in that hits the tapered portion inside the drain pipe and gets forced
against the inserted pipe. *If the fitting on the inside end of your
copper drain is cone shaped (gets smaller as goes in) the plastic
tapered washers and the flat rubber washers are going to be tough to
get a seal. *You may need to dig through the trash and find the old
nut. *

Ah, that may be the problem...

Unfortunately, the nut was seized on to the copper fitting, I couldn't
move it with an 18" pipe wrench, so I had to split it off. The nut is
no more.

If you tried and failed with so much force, the copper pipe is
probably distorted and will not seal with the "rubber" seal any more.
I would glue on a PVC connector to the copper pipe with one of the
resin glues. You will need a thorough clean up on the pipe.