Welding, brazing, and soldering are the three methods creating a sealed connection between copper pipes. The intense amount of heat needed to weld copper pipes makes it difficult to perform outside of a controlled shop environment. Brazing, like welding, requires a high amount of heat, and is used on pressurized copper refrigeration lines. Soldering requires the least amount of heat, provides a water tight seal and is the standard connection used for residential copper water supply lines.
Remove the emery cloth from the copper pipe. Examine the pipe's end. If it is shiny, place the length of copper pipe aside, and repeat steps two, three and four with the other length of copper pipe. Insert a pipe brush into one end of the coupling.
Slide the coupling onto the cleaned and fluxed end of one of the copper pipes. Insert the other cleaned and fluxed pipe into the empty side of the coupling. Straighten 12-inches of solder. Bend the last three inches of solder to a 90-degree angle.
Bump the solder against the edge of the coupling. When the solder draws into the coupling, run solder around the edges on both sides of the coupling.