Bruce, if you can't unscrew the plug, instead of messing about with old
lead, oakum and frozen threads it might be easier to just hacksaw
(actually I urged mine with a sledge) the clean out off and replace it
with a PVC fitting using adjustable vinyl compression couplings.
Real plumbers are laughing to keep from crying.
Turn to Safety, Arch
Fortiter
http://community.webtv.net/almcc/MacsMusings