When doing an inspection: 

Always get a sewer scope!

A sewer scope is an additional inspection that costs about $200 but is one of those things you don't want to buy a house without knowing.  During a sewer scope they put a camera down the sewer line to see if there is any damage to the line.  Often they find tree roots that need to be removed but other times they can find actual damage or whole collapsed lines.  The cost to fix them can run in the tens of thousands of dollars and become your problem after the close so you need to know about them before hand. 

Let me tell you a little story:

Several years ago a friend of mine was selling her house.  The potential buyer did a sewer scope and found a complete collapse.  The estimate to fix it was in the neighborhood of $40,000.  That's a 4 with 5 zeros!  Something you would certainly want to know. 

Side note: 

The scope isn't necessary for condos since the association is responsible for the maintenance of the sewer line for condos and co-ops.

Just like a regular inspection and a title search, you hope they show nothing and they typically do, but when they do find something it makes the $200 you just spend seem like candy.