Galvanized pipe is steel pipe that has a zinc coating that prevents corrosion of the steel. Galvanized pipe can be cut and threaded to accommodate threaded pipe fittings made of galvanized steel, copper, plastic, or a variety of other materials. Before cutting any length of galvanized pipe, first check the ID of the pipe with a magnetic tool. If it's not available, use clear, unmarked vinyl tubing as a substitute. The coating on galvanized pipe is thick enough that you cannot drill holes in it with a standard bit. However, if the pipe is uncoated stainless steel, it can be drilled like regular steel pipe. Drilling galvanized pipe requires special techniques because the coating will break off when hit with a hammer or punch. The coating also contains zinc, which dries into a hard scale that can block up your pipes. Therefore, before drilling any length of galvanized pipe, have a certified plumber test each joint for water flow using a pipe tester. Also, make sure to wear protective clothing and equipment due to the risk of exposure to zinc during this process. If you are lucky enough to find some galvanized pipe in unused locations such as old plumbing under the flooring or inside walls, you can usually remove the coating by blasting the area with sandpaper wrapped around a soft brush or stick. Make sure to clean out any powdery residue left behind after removing the coating.