If you own (and especially if you are selling) or are buying a home that was built before 1980 (or even later), sewer line protection is very inexpensive (under $70/year) and worth it given the cost if something does go wrong. Water line protection is not as critical but it too is inexpensive. Below are the links to where you buy it and a newspaper article that will give you comfort that this is not a snake oil scam.
Link to USP Website
Link to Informative Article