A possible addition to this article: In Canada, at least, there are often numerous cleanouts on each branch off the main sewer line, generally tucked behind cabinets. Thus, if only the sink (toilet/shower/whatever) is blocked, or if only the one bathroom is blocked, you can use the clean out for the sewer line directly from the problem area, rather than having to go through the entire house, which saves you a lot of time (and money, if you're paying your plumber by the hour). I kind of expected this would be standard since it's the easiest way to get access to a specific branchline where the problem is; steering augers into the proper path of a junction is a royal pain.
@anon167424 (The guy with the sinkhole issues): I'm afraid the city doesn't really know what it's talking about. The presence or absence of an opening that gives access to the sewage line into your home is irrelevant to the geological forces that cause sinkholes to develop. There are a number of other things that might cause it:
Natural ground conditions from the natural erosion of limestone or other rock types that are similarly susceptible to water erosion. Sinkholes are just like caves; they just open up rather than sideways.
Poor foundations. Standards for road construction are awfully poor in North America. Whenever there's a major flood incident, you'll see lots of footage of roads that have been washed out, particularly when they're over fill (rising above the natural ground). The powers that be refuse to understand this and keep rebuilding the roads the same way, which leaves geologists more than a bit annoyed. If you have a lot of groundwater activity in the area, the foundation issue would cause a sinkhole.
Broken pipes. Same issue with the foundations as above, but an old sewer or water line that breaks is going to leak large volumes of water. So, even if you don't naturally have a lot of groundwater activity, you now have far more than nature would ever throw at you. And in the case of a leaking water main (pressurized to 60 psi in my hometown), it only takes a day or two to cause critical damage.
And unfortunately, no, the city's not going to be liable. They installed the pipes properly -- just a long time ago and they need new ones. They built the foundation of the roads to spec, except the specs are useless.