Cast-iron drain pipes, although very strong and durable, need to be maintained. As a part of that maintenance, they should be cleaned on a consistent basis to prevent various types of dirt buildup and clogs that may form after time. These pipes cannot be cleaned with just any methods. There are specific items to use that will stop more damage from being caused.
Drain cleaners are generally made of various chemicals that dissolve the dirt or grease buildup in the drain pipe. There are many different types. Purchase a drain cleaner from a hardware store, but read all of the labels and instructions first. Some are not designed for cast iron. If the wrong type of chemical is used and doesn't drain correctly, it will start to erode the iron. Diluted chlorine bleach is one chemical that can possibly be used, but there are differing opinions on it because if it stays in contact with any sort of metal for a long time, it can cause corrosion.
Professionals use stronger types of drain cleaner, and it is recommended that if this type of cleaner is necessary, to hire a qualified professional to do it for you. If you are going to do it yourself, wear protective gloves and goggles to prevent chemical burns to your eyes and skin.
How you remove the clog depends on where it is located. If you are only having problems with one drain area, it is most likely in that pipe; however, when more than one is effected, then it is probably one of the main pipes. Remove the drain cover of the pipe that is having problems and look down to see if you can locate the clog. You may simply be able to remove it from there.
Use a plunger over the opening to plunge the drain pipe. It may take a few tries, but it should bring the blockage up far enough for it to be removed. Proceed to pour some appropriate drain cleaner down the pipe to remove any other dirt or grease buildup. Replace the cover and start to collect water in the basin. Remove the plug and let the water drain to see if the water is flowing normally again.
If you don't have one already, invest in a drain snake. This is a tool used by even some professionals to clean a cast-iron drain pipe, and it isn't expensive. It is a long flexible device made from metal that curves around the corners of the drain.
Push the snake down the drain, and when you hit an obstruction, twist it so that the snake goes right through it. Remove the snake and flush the drain pipes with water.