If you main drain lines are galvanized steel, (it's more often cast iron) then there may not be much you can do except repipe. While they can last a very long time, depending on the situation, they can fail early on. They tend to rust from the inside out, and that rusty interior gets very rough which snags all sorts of things easily (hair, lint, etc.). CI could last a century, or not. It's hard to say how long plastic pipe will last, but it could be a very long time as well. At least it doesn't rust!