How to Solder Copper Pipe
Clean the pipe with a wire brush.
Clean it to bare metal.
Apply flux paste.
The flux paste ensures a clean surface for the solder.
Use a handheld propane torch to heat the fitting.
Just don’t get it so hot that you can’t hold it any more.
Melt the solder so that it flows into and fills the joint.
Finally, using a soldering iron, melt the solder so that it flows into and fills the joint between the pipe and the fitting.