Call a decent plumbing contractor and have them water jet these lines with hot water
(Below 160 degrees F.)
Using bleach is great for killing mildew and mold BUT it may kill the good bacteria like anaerobic germs that some of these systems depend upon to break down solid waste.
Water Jetting will scrub these lines to a like new condition ESPECIALLY Cast Iron.
Cast Iron pipe is the best of the best for waste piping in the majority of applications.
Water Jetting is safe and no harmful chemicals are used.
If you have any questions please feel free to E mail me