Caution 3: You cannot have any water sitting in the pipe when you unsolder it: You can hold the torch to the fitting endlessly, but it will not heat enough to break the solder loose.
Try jiggling the pipe enough to get the water to drain, but if it doesn't, you might have to either cut the pipe or drill a hole to drain the pipe.
Turn Off the Taps Modern plumbing has made it easier than ever for us to get clean water—and to waste it.Third of an eight-part series on bathroom remodeling (The first and second parts of this series explain how to demolish your old bathroom.) What would a bathroom remodel be without a little plumbing work?Very likely, you will need to make changes both on the supply side and the drain side.There's more to proper plumbing than just following the codes and rules.Planning and installing a system that's quiet, efficient, and leak free is something of an art.
Caution 1: Because you are torching amongst the studs and drywall, be very careful. Buy a heat-resistant cloth at a plumbing store or at The Home Depot -- in the tool area where they sell propane torches -- that you can drape over the studs. Caution 2: Soldering at the valve can damage the ceramic disk inside the valve.