Unless the system was inspected in the last three years, or built within the last five years, anytime you plan on selling, adding on, or doing maintenance that require a building permit, the local unit of government will require a compliance/septic inspection.
A compliance inspection will examine your septic system or holding tank to ensure that it is watertight with no cracks, leaks, or root invasion. The inspector will also look at the type of soil your system is in, make sure requirements are met, and address any setback issues. This must be done by a licensed inspector who will then complete and submit a Certificate of Compliance to the homeowner and the local unit of government.
A compliance inspection is to ensure a septic system in is compliance. It does not warranty or determine the longevity of your system.