Galvanized Pipe is a word we commonly hear in the real estate industry - especially during home inspections. Galvanized piping is a steel pipe coated with zinc that was thought to resist rust and corrosion from exposure to water or the elements. It became a popular fixture in American homes because of this thought and it was commonly used as water supply piping or for outdoor appliances and structures (such as fencing). It turns out that this type of pipe is prone to rusting from the inside of the pipe, as I observed from this piece removed from my son's home this summer. This rust can potentially contaminate the water supply in addition to constricting the water flow and in the worst cases can cause the pipes to burst.
There is mixed opinions on whether this type of plumbing fixture can be maintained or should be replaced. I found these instructions on eHow.com for cleaning of galvanized piping.
1 - Check to see whether there is a rust problem in the galvanized pipes. It will be clear if you have a buildup of rust in the pipes as the flow will be badly constricted and the water supply may be reduced to a trickle.
2 - Purchase a chemical pipe cleaner. A product such as this should have the required power and effectiveness to wash away the rust when you apply it. Chemical cleaners are readily available at most hardware stores.
3 - Apply the pipe cleaner to the pipe. Instructions may vary depending on which brand of pipe cleaner you have bought, so follow the instructions on the bottle and apply the pipe cleaner. Leave the cleaner to circulate for as long as instructed on the bottle.
4 - Rinse the pipe with water. When the pipe cleaner has circulated in the rusted pipes, run the taps and let the water rinse the pipes. After a small amount of time the water supply in your home should be less constricted.