Well, for anyone who saw the other thread, I did call a plumber and he used channel locks to get it off. The last time I got fierce with plumbing I seriously regretted it, so I just wasn't willing to yank on something I didn't understand. Well at least I had some good coupons.
Anyway, new question: He says I should use bio-clean, which conveniently, they sell. Anyone have experience with enzymatic drain cleaners? Are they worthwhile? Can I use a cheaper one like Zep or do I have to shell out the big bucks for BC?