Determine a location for the valve on a water line in or near a heated area.
Shut off the main valve where water comes into the home. Open the lowest fixture in your house to drain out any water.
Use a pipe cutter to remove the desired section of pipe (Image 1). Rotate the pipe cutter around the pipe, gradually tightening it until it cuts through. Place a bucket underneath the cut area to catch any water remaining in the line. Clean any burrs from the end of the cut pipe with steel wool.
Temporarily remove the petcock (small screw) from the valve (Image 2).
Be sure to install the valve in the right direction. An arrow points in the direction of the water flow.
Cut a section of 1/2" copper pipe to the appropriate length. Allow a little extra length for a good fit. Make sure the new pipe is the same diameter as the existing water line (usually 1/2").
Use steel wool to clean the pipe end and inside the stop-and-waste valve.
Use a propane torch to heat the fitting and the pipe where they connect. For best results, hold the edge of the blue flame right against the pipe.
Push approximately 2" of solder into the joint where the valve connects to the pipe. The heat will melt the solder and allow it to seep into the connection. Solder completely around the pipe-valve connection.
Practice the soldering technique on scrap pieces of pipe and copper fittings before trying it on the valve.
Use the same soldering techniques to install the new assembly to the water line.
Depending on the installation, it may be necessary to use inexpensive copper fittings to connect new sections of pipe to the existing water line. These fittings are widely available in different configurations and diameters.
Replace the petcock, and open the main water line to check for leaks.
Before temperatures dip below freezing, shut off the valve, and open any spigots that are "downstream." Then remove the petcock screw to drain the pipe.
If any sections of pipe "upstream" of the new valve are in an unheated area, cover them with foam pipe insulation.