Normal home inspections won't reveal the true condition of the buildings Drainage pipes that are underground. The only way to obtain the true condition of these pipe's is by using sewer cameras to actually look inside and down the length of these Drainage systems.
Common Problems with cast iron pipes.
Rust and Corrosion
Because cast iron pipes are generally thick-walled,and corrode from the inside out, corrosion will form on their interiors causing problems with drainage. After a number of years, however, the rust level inside cast iron pipes will increase to the point that water flow is greatly decreased or even blocked all together. Removing this corrosion can restore water flow in most cases.
Uneven Pipe Surface
Another common problem with cast iron sewer pipes is an uneven interior surface. Over time, hard water can cause build up inside of pipes. The resulting bumpy texture creates the perfect environment for hair, paper, grease and other debris to get caught, eventually resulting in problematic clogs.
Aging cast iron pipes can form cracks that allow tree root intrusion allowing root systems to form inside of them, slowing down and eventually blocking the flow of water.
What to Do?
If you live in a home with cast iron sewer pipes, its a good idea to have them inspected. Modern plumbing technology offers a number of solutions for problems with cast iron sewer pipes that are both effective and long lasting.