If you are buying a home with a septic system, private or shared, you should consider having it inspected by a professional septic company. Our standard home inspection does not include this type of specialized, intrusive inspection. As well, the State of New Hampshire requires a certified Septic inspector. To properly inspect the system, the septic company will need to dig holes to access the underground parts of the system. This will include inspecting the tank, as well as the leach field.
Private Septic System
Even newer systems can have hidden problems. Damage from driving over parts of the system, misuse by pouring paint down drains or components settling and shifting are a few things that can go wrong with a system that you would think is new and of no concern.
If a brand new system has been installed, the tank is likely not full yet for a proper flow test (water leveling the house, entering the tank, then leaving to the leach filed). In those cases, you should find out what warranty there is, if it is transferable to a new owner and how long it is. Then, about a month or two before the warranty expires, have the system inspected!
When possible, you should have the sellers identify the location of the septic tank cover and leach field. This is more of an issue in the winter when to ground is too frozen to "probe" for these underground components.
Public Sewer System
The sewer line that runs from a home to the main sewer line in the street is the homeowners responsibility. Checking this section of a sewer line is not part of a home inspection.
In homes that are older and have cast iron, clay or matted drain pipes, these lines can be clogged or damaged. If you see that the home has a cast iron line going through the basement wall, or the home was built prior to 1970, it may be in poor condition. You should consider having a septic company run a camera through the line to inspect its condition. Replacing these lines can be just as expensive as repairing a septic system.
You can also inquire with the sellers or the town, to verify if the line has ever been replaced. This may be true with much older homes of 100 years or so. Make sure there is a clear understanding between the town replacing just the street sewer lines and the lines running to the house!