Is there any product out there that can help in loosening stubborn fittings. I have a steel drain pipe that has a copper fitting screwed into it and the nipple has corroded and It is too tight to wall to resolder so I would like to take the copper fitting out of the steel sewer line and replace with plastic and replumb. The 2 dissimilar metals probably has corroded and it is making it tough to turn out. I have tried liquid wrench and heat but no movement and Have a wrench on it with a lever. Any suggestions???