text: To make a solder connection, a chemical flux is applied to the inner sleeve of a joint and the pipe is inserted. The joint is then heated, typically by using a propane or MAPP gas torch, although electrically heated soldering tools are sometimes used. Once the fitting and pipe have reached sufficient temperature, solder is applied to the heated joint, and the molten solder is drawn into the joint by capillary action as the flux vaporizes. "Sweating" is a term sometimes used to describe the soldering of pipe joints.
  Where many connections must be made in a short period (such as plumbing of a new building), soldering is quicker and less expensive joinery than compression or flare fittings.   A degree of skill is needed to make several reliable soldered joints quickly. If flux residue is thoroughly cleaned, soldering can produce a long-lasting connection at a low cost.  However, using an open flame for heating joints can present fire and health hazards to building occupants and requires adequate ventilation.