It has been my experience that what you cannot see can hurt you when it comes to your home. One area that is often overlooked is the sewer line to the city or town system. As a home inspector I often look at the front yard for large trees which are likely to have deep roots. These roots are often found growing in the septic line if the trees are big enough. Hardwoods are particularly problematic as the roots drive way down to reach the water source. If I feel there is a potential problem with tree roots I will recommend a sewer scope.
Sewer scopes are usually owned by towns and cities and can be preformed for about $150 – $200. The scope is simply a camera on the end of a long snake that allows the operator to watch a screen as they push the camera through the cleanout in the basement drain. If problems are encountered they are noted and sometimes even videoed so you can see for yourself what the problems are. Most sewer problems are separations in the pipe but other problems can include sags and tree roots. If you are buying a home and you notice a sewer snake in the basement it may be smart to get a scope done. Often times partial problems can be resolved using a snake but rarely will the problem go away.
If the sewer line is partially blocked it is usually due to the above mentioned reasons and it is also likely that soon a snake will not help. In fact if the pipe is separated the snake could push through the opening and cause a greater blockage of clay. My opinion is that it is best to know ahead of time so you can anticipate the $3000 – $4000 repair of the line when it needs to be dug up. Of course this usually happens when there is four feet of snow and temperatures of -30.