to properly make a good solder joint,first there must be no water in the pipe or fitting,then both surfaces should be cleaned with steel wool.apply a layer of flux to the pipe(powerflow or any self cleaning flux should do)and insert into fitting giving a little twist to ensure both surfaces are coated with flux,heat with a blowtorch until you see a ring of solder appear and add a little lead free solder to make sure but do not add solder until you see the solder appear between the pipe and fitting.
steeveepee, December 2008
