If you are buying a home with a septic tank, you should consider having it inspected by a professional septic contractor. My standard home inspection does not include this type of specialized, intrusive inspection. I recommend that you hire the company that has been maintaining teh system and pumping teh system for the past several years.  THey can explain the condition of the field, any repairs or upgrades and the history of pumping the tanks. To properly inspect the system, the contractor 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.

It makes good sense to have the tank pumped at the time of this inspection. A professional septic contractor can perform both the inspection and pump the tank, killing two birds with one stone and assuring that you begin with an empty tank and a system that has been inspected. Often, you can negotiate with the seller to have them pay for the pumping.