I am replacing a thirty year old bathroom sink. I have been unable to loosen the drainpipe that comes out of the wall. The coupling seems to be rusted to the pipe. Any tricks to resolving this problem?
Apply penetrating oil, like Liquid Wrench or spray with WD-40. Tap the pipe to set up vibration and let it work. (You may have to repeat this several times). Then loosen the joint with a wrench and good leverage.
It is very possible that the pipe is soldered into the connection, unless there is an obvious slip nut. If so, then you have to chop the tubing out of the connection and then saw the brass adapter out of the pipe, (carefully). Then you have to install a new pipe and compression coupling to adapt to the trap.