My Williamstown house is over 100 years old. Will the original drains still be in use?
Very often, yes — at least in part. Many Williamstown properties still run on their original earthenware clay sewer lines, sometimes with sections replaced piecemeal over the decades. That mixed condition is why a CCTV inspection is worth doing even when nothing is currently blocked: it tells you what material is down there, what condition it is in, and whether you are looking at routine maintenance or a line approaching the end of its life.