What should be done before applying solder to a copper pipe joint?

Before applying solder to a copper pipe joint, cleaning the joint is essential for ensuring a strong, leak-free connection. This involves removing any oxidation, grease, or other contaminants from both the pipe surfaces and the fitting that will be joined. Clean surfaces help the solder adhere properly, allowing for effective capillary action to occur during the soldering process.

Proper cleaning can be achieved by using a wire brush, emery cloth, or a similar tool designed for copper. This step is crucial because any dirt or oxidation can prevent the solder from flowing smoothly into the joint, resulting in a weak bond that can lead to leaks over time.

While wiping the pipe with a cloth might remove some surface dust, it doesn't address oxidation or residues. Measuring joint diameter, though important for fitting purposes, doesn't specifically affect the soldering process. Heating the joint is a step that happens later to facilitate the melting of the solder but must only be done after ensuring that the joint is clean. Therefore, cleaning the joint stands out as the necessary preparatory task before soldering a copper pipe joint.