Plumbing Q: loosening tube stuck in stub out

I am trying to replace the entire p-trap assembly under my bathroom sink. My problem is that the old drain extension tube (the part that connects the trap to the stub-out) seems to be stuck in the stub-out. The stub-out is cast iron and the old tube is some kind of thin metal (yes, I am a plumbing novice.) What is the best way to remove the tube from the stub-out without breaking the tube? Twist? Pull? Do I need a torch or chemical to loosen it?
thanks, Tony
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Anthony L. wrote:

In days of old, a "solder bushing" was used to connect the thin brass tubular trap arm to the "stub out". The bushing is threaded on the outside and smooth on the inside. The trap arm is first cleaned of the chrome plating and then its brass surface is soldered to the bushing ID. Then the whole mess is screwed into the stub out (which in this case is probably galv or brass).
Anyway.........if that's what you have, the fix is to saw off the trap arm as close to the wall as possible. Then use a hacksaw blade (or a small recip) to saw lengthwise thru the bushing. That will weaken the bushing to the point where it can be unscrewed. Usually they are in so tightly that you can't just unscrew it and there is nothing to grab on either.
To make a replacement, get a "DeSanco" fitting of the correct size. It will screw into the stub out and has a ferrule adapter for the new trap arm. ------------------- Doesn't sound like you have copper DWV piping, but in those cases it was common for the trap arm to be soldered directly into a brass fitting (no threads).
Jim
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I went through 8 plumbing and home repair books and searched the web but couldn't find any information about this situation. Thanks Jim, you are a godsend!
Tony

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