In this tutorial, we learn how to solder copper water lines. First, take a sand cloth and thoroughly clean the outside of the tube. Then, take a cleaning brush and clean the inside cup of each side of the fitting. Apply flux to the inside of the fitting, then insert the tube inside. Make sure the tube is inserted into the bottom of the cup properly. Now, take a torch and apply the head to the cup of the fitting. Wait until the solder starts rolling and goes all the way around the fitting. When finished, clean off the pipe and you are finished.