My old tub has an old steel drain and broken linkage. How do I remove the linkage and how do I remove the drain from the bottom of the tub. It is steel and seems to be set right in there for life. I would like to replace it with a pop-up stopper but for the life of me I can't figure out how to get the old one out. Does it unscrew so that I can screw in a new pop-up unit? If so, how do I get it started. This is an old but very functional and clean tub - I have put in a new tub surround etc., and this is the last piece I am fighting with.