I'm installing a sink, faucet & garbage disposal. Got the sink in, new shut
off valves, faucet installed & working, all fine so far. BUT the new sink's
drain hole is in a different position that the old one, basically right
above the ABS drain line as it runs under the sink to where it had attached
to the old drain (new sink is single bowl, old was double). There is not
enough clearance between the drain line & sink bottom to fit the disposal,
so I need to re-route the drain line. There's a white ABS stub (it's white,
I'm assuming it's ABS. House is about 30 years old) sticking out of the
wall about 2-3 inches, not much exposed. Black plastic pipe is glued to
this to form the old drain line. Ideally, I would like this old black line
to "disappear", leaving the bare stub, to which I would glue a new line
routed as I need. I've never dealt with this kind of pipe before. How d I
remove the black section from the white stub, leaving the stub as long as
possible & ready to receive the new drain? Any tips as to working with this
material appreciated!

Thanks

Dan