With the parts fluxed, fit them together and support them on a solid, non-flammable surface. You do not need to fit together every single piece and solder it at once, and in some instances it will work best to solder one fitting at a time, allow it to cool, and then flux and fit together subsequent parts. In some instances, when you are working on fittings being added to an existing plumbing system, it may work best to assemble all the parts at once, in order for them to fit into place, and then solder them after all are assembled.
If you are soldering fittings on an existing water supply line, keep in mind that it is imperative that you shut the water supply valve off and drain all of the water from the pipes being worked on before attempting to solder in a new section. Removing all the water from a system can sometimes be quite difficult and time consuming, and it can help the system to drain if you open the lowest valves in the system that you can find, such as outdoor hose bib faucets, as it vents the system and allows the water to drain. If even a small trickle of water seeps into a pipe or fitting that you are trying to solder, the resultant steam and the cooling effects of this water make it virtually impossible to solder the fitting properly. To temporarily plug a pipe to keep water from seeping into a fitting being soldered, I have heard of some plumbers using white bread, forced down into the pipe to plug it long enough for the soldering to take place. After soldering, the bread tends to dissolve when the water is turned back on. You can also buy special plugs that are made for the same purpose, and later dissolve when the water supply is turned back on again.
Safety Goggles: Many things can happen while soldering that could place your eyes in jeopardy. Acidic flux could drip or splash into your eye, or an impurity in the solder could cause this hot metal liquid to splatter as the torch flame is heating it. It is always advisable to wear eye protection when soldering.
It is best to start soldering by using a flame that is not too intense. Overheating the pipe is counter-productive as the solder will cease to flow properly. You want a blue inner portion to the flame, as seen here, but avoid using a flame that is extremely loud and hot. As you heat the pipe and fitting, concentrate most of the heat on the fitting, as it is allows heat to dissipate from the fitting to the the part of the pipe that is inserted inside it, heating both more evenly. Also, move the torch flame from side to side, so that the heat is not totally concentrated on one spot. If you can heat the fitting from only one side, it is best to use a low flame, and give the heat time to spread evenly throughout the fitting. DO NOT hold the solder wire near the flame as you are heating the fitting. In order for the solder to properly bond to the copper surfaces, it must melt from contact with the heat of the copper itself, and not be melted merely by being stuck into the flame of the torch. The solder wire is never put in contact with the flame, and in most cases the torch flame will be removed from the fitting after it is heated so that you can go about the task of soldering it.
NOTE: heat from the torch flame can cause the pipe to get VERY hot throughout its length. Do not assume that the pipe will remain cool enough to handle just because you grab ahold of it a foot or more back from where you have heated a fitting, since it almost certainly will burn you. Wearing leather gloves is always a good precaution. The heat from the torch is also an inherent FIRE DANGER. If the torch flame is not carefully controlled or is misdirected, it can quickly cause any combustible material to ignite. This can be especially dangerous if you are working in a confined space, such as the crawlspace of a house. Often, water has been shut off in order to facilitate work on the plumbing, so a handy garden hose may not be available to put out a fire. Keeping a fire extinguisher on hand is always a good safety measure.
In order to tell when the fitting is hot enough to take the solder, I tend to occasionally tap the end of the solder wire on the joint. If the joint is hot enough, a small bit of solder tends to quickly melt off the tip of the wire, and get sucked into the joint through capillary action. At that point, you know that the fittings are hot enough, and can quickly run the end of the solder wire along the joint of the fitting, as seen here. The solder will immediately melt and be drawn into the joint. You do not want to over-do it, because doing so can create a large deposit of solder within the pipe, clogging it or reducing the water flow, or creating turbulence/noise issues within the pipe.
Fittings that are properly cleaned, fluxed, assembled, and heated tend to draw in the liquid solder very efficiently, creating 100% coverage of solder within the joint very quickly -- quite often even when the solder wire is applied to only one part of the joint, due to the capillary action that sucks the liquid solder into the joint and distributes it. When done properly, you will be able to see that a soldered joint is a beautiful thing, and the use of galvanized threaded pipe, and all of its pitfalls, may seem all the more unappealing to you.
