TY for that - and will do.
Since posting, above, have spent some time digging through the 28 pages of older posts and have had some luck in getting guidance on the issue.
Seems that I do have a 'push-out'-type plug, since it definitely lacks the two holes beside the nipple hole that would be used for inserting whatever tool was used to turn the plug.
So, short of the plug being 'epoxied' in, its likely to be a case of putting something in there to eat away the rust(?) and/or release its grip - in the meantime, I'm off to the Home Depot to get a nice piece of 3/8" steel rod so I can pound it out a bit more violently than with the 1/4" bronze rod I have used.
Besides, it must be made an example and be punished and beaten into submission for daring to challenge my authority! Once its loose and cleaned-up all will be forgiven.