How can I get a bathtub stem out? It will tighten up, but when unscrewing it just turns forever. Is there a trick to getting the stem to unthread? HELP!

First of all you're going to hafta be more specific. I'm assuming that you have a 2 or 3 handled tub and shower faucet that you want to change the washer and can't remove the stem and washer assembly. If this is so get back to me with more details. Using the image I put up tell me where you are and what you have done, regards, Tom