I'm buying a mid-70's house in Florida with cast iron sewer lines. I had it scoped and no problems were found (luckily, as the pipe runs through the concrete pad). The plumber said the walls of the pipe were rough from age and build-up. He suggested hydro-jetting it to keep it running smoothly, and that would give him a better look at the condition of the pipe. I'm not sure this is necessary. Is this commonly done? It's not cheap, about $2k.