Cast iron pipes were once a mainstay in household plumbing systems. Today, however, PVC has mostly replaced cast iron. This is because cast iron, through regular use and age, tends to corrode on the inside, causing the inner surface to become rough. When this happens, material flushed through the pipes will flow as smoothly as it should. Eventually, this causes a buildup of debris that blocks the pipe altogether. Fortunately, clearing a clog from a cast iron pipe requires the same basic tools and know-how needed for unclogging other types of pipes.
Locate the cleanout plug for your cast iron pipes. In most cases, the plug is in the basement, in close proximity to where the cast iron pipe enters and/or exits the cellar wall. If the cast iron pipe does not have a cleanout plug, locate the slip-nut that connects one section of cast iron pipe to the next.
Position a bucket or other large container below the cleanout plug or section of pipe that you plan on removing. Slowly loosen the plug or slip-nut using a pipe wrench. Be prepared for some water to spill from the pipe. Allow the water to drain from the pipe before completely removing the plug or slip-nut.
Place the tip of the plumbing snake/auger into the cast iron pipe. For most snakes, simply crank the handle clockwise to begin unwinding the cable. As the cable unwinds, push it through the cast iron pipe.
Continue pushing the snake through the cast iron pipe until you feel it coming up against the clog. Push the snake forward in order to break through the blockage and then pull back slightly before pushing the snake forward again. Do this several times in order to ensure that as much of the clog is removed as possible.
Attach a high-pressure nozzle to a garden hose and spray water down the cast iron pipe. This will help remove any remaining debris and let you know whether the water is draining as it should. If the cast iron pipe is clear, go ahead and replace the plug or section of pipe. If not, continue snaking the pipe until it entirely removes the clog.