Wanna save $20-50k on buying a new home in Seattle? Get yourself a sewer inspection before you make an offer!
In Seattle (and maybe other municipalities, I don’t know), the homeowner is responsible for the sewer system all the way up to where it connects to the sewer main. It’s called your side sewer, and it runs from your home, underground, to the sewer main that’s under the street or in an alley.
It can run underneath your foundation, lawn, sidewalks, driveway and the street itself, and that’s where the potential costs come from. If you have to repair or replace it, the pipe itself is cheap, but tearing up and then rebuilding, say, a section of your street (which is how it goes), can run tens of thousands of dollars.
When we were looking at the house, our real estate agent recommended a sewer inspection, which is performed these days by way of digital camera on the end of a long line – a sewer scope.
Rick Delamare was a consummate pro – extremely knowledgeable, friendly, and, lucky for us, very well versed in dealing with the City of Seattle. Other than a few roots starting to poke into the pipe here and there, this was the big issue he found:

This photo is from a video we got, and it shows our sewer pipe in the foreground and the sewer main in back. The +087.5′ means the scope has traversed 87 and a half feet from of pipe from the point where he hooked in to the system, in this case, 20 or so feet underneath the middle of the street. You can see the pipes are offset – they don’t line up, and it’s right at the junction between the side sewer and the main.
If we hadn’t seen this, we could have had a backup eventually, and we likely would have had to duke it out with the City of Seattle, arguing about who was responsible. But since we had the inspection, we got the city to come out preemptively to do their own inspection, document the problem, and send us a letter acknowledging this issue is their responsibility. (Rick had given it a 95% chance of playing out that way, in his opinion.) So now if there’s a problem down the road, we’ll only have to deal with raw sewage backing up into our house, rather than also fighting over costs with the City of Seattle. Yay?