As a renter you can blithely assume the obvious parts of the home you live are all you need to know about. As an owner, if there are issues with the flow of your household plumbing, including the line to the street, you will be dealing with them. And paying to repair them if necessary. These are not repairs that can be postponed without consequence.
The city (San Francisco Public Utilities Commission- SFPUC) is doing a lot of sewer repair work on the city lines, but property owners are responsible for their lines ("sewer laterals") from the building to the city lines, and for replacement of the sidewalk squares that have to be removed for repair and/or replacement.
Old clay pipes shift as the earth does in our seismically alive neighborhoods, so if you can actually pull off an inspection contingency in this market, (or better yet, pre-inspect) a sewer lateral inspection is a really good idea. It's kind of cool, they run a tiny video camera down the line, and you can watch if you are not squeamish. Though as a buyer you don't have much leverage for repairs or credits these days, it is so much better to know up front what you are getting into. Sewer line and the corresponding city sidewalk repairs can range from a few hundred to many thousands of dollars.
