A cast iron pipe may be lining one of the walls of your basement. Many American cities used cast iron pipes for years as the pipes that ran waste from the home out to the sewer system. Cast iron pipes are generally strong and can last for a very long time.
However, some of the gases and chemicals that flow down a cast iron pipe can react with the pipe and create sulfuric acid. Gases such as hydrogen sulfide can trigger the reaction, or some of the chemicals in household cleaners already contain small levels of sulfuric acid. Sulfuric acid can corrode a cast iron pipe from the inside and cause it to rust through.