Copper pipe is installed for the supply of both hot and cold water, with the pipe sections joined together with soldering paste, couplings and melted solder. To cap off (seal the end of) a copper pipe, an end cap is soldered to the end of the pipe. The cap is roughly half the length of a straight coupling, with one end closed off. Later, if needed, the cap can be cut off and more copper pipe joined to the existing line.
Cut off a 4-inch section of 120-grit emery cloth using a utility knife or scissors. Wrap the cloth at a perpendicular angle around the outside of the pipe end, turning it several times around the pipe until the pipe surface becomes shiny. Push a circular wire brush into the copper end cap, rotating the brush several times.
Brush a thin layer of soldering paste (flux) around the shiny end of the pipe. Also brush paste onto the inner walls of the end cap. Push the end cap fully onto the copper pipe. Pull an 8-inch section of solder from its roll, and turn on the propane torch.
Heat all around the sides of the end cap until the flux begins to sizzle. Touch the end of the solder to the seam where the pipe enters into the coupling. If the solder melts, apply approximately 3/4 inch of solder around the seam -- capillary action will draw the solder between the end cap and pipe.
Wipe off all solder drips and flux residue from the pipe and end cap using a rag, but be careful because the surface will be hot.
Make sure the end cap is the same diameter as the existing copper pipe. Allow no water in the copper pipe near where the end cap will be fitted, as the propane torch will not be able to heat the pipe to the correct temperature to melt the solder.