Put it on Craigslist with a note that the recipient will
need to take it out themselves. It should be gone
by noon.
I've broken up tubs with a large sledge, but it's a lot
of work, and that's on a solid floor. In your case your
likely to take the counter with it. The only other good
way to cut cast iron that I know of is with a carborundum
blade on a circular saw. Wear glasses, mask and heavy
pants. Take the batteries out of the smoke alarm. Then
dig in and enjoy the fireworks of sparks and smoke.