Step 4 · Clean Pipe and Fitting Surfaces
A successful solder joint depends on perfectly clean surfaces. Use a strip of emery cloth or specialized sanding cloth to thoroughly clean the outside of the pipe end, extending about 1 inch from the end (or slightly more than the depth of the fitting socket). Sand until the copper is bright and shiny, with no signs of tarnish or discoloration. For the inside of the copper fitting, use a wire fitting brush of the correct diameter. Insert the brush and twist it several times until the interior surface is also bright and shiny. Do not touch the cleaned surfaces with your bare hands, as skin oils can interfere with soldering.