If you're reading this page and you have "city" sanitation then you've probably got nothing to worry about. Well not much, exceptions might be if a tree has invaded the pipes there may be an issue, but usually "city" sanitation just works. That said, some cities with older housing stock require a "sanitation inspection", an example might be Pacific Grove.

If you have a septic tank then you need to look carefully at what you've got or are getting. Septic Systems have been around for a long time and they work well, but they need to be maintained. I've lived in a house with a Septic System for more than 10 years and apart from "having it pumped" it seems to work just fine with minimal maintenance.

By way of maintenance, I flush a maintenance enzyme into my septic system every six months or so, and have it pumped every 5 years. When it was last pumped, I was told it was working just fine. 

I also located an EPA document that you might find useful - EPA Homeowners Guide to Septic Systems