If it is the first time you are soldering copper pipe remember; clean and dry. If you don’t clean the pipe where the connection is being made it will leak and then you will have to drain the entire line and start over. Time is valuable so take the time to do it right. Make sure all of the water is drained from the line before starting your project. After shutting off the water you can insert white bread into the line to soak up the water ( no crust). Sand all the parts clean and bright and apply flux to the pipe immediately. Then when you solder you will get a good seal. Remember you are to heat the connections with the torch not the solder. A properly soldered connection will suck the solder into the joint.