Some very good info here. As stated, septic systems are normally maintenance free. All I would add is to be cautious of the amount of laundry bleach that goes into the system. Bleach tends to kill off the working waste enzymes. Replacement enzymes (Rid-X or similar) need to be added with higher bleach use.
Our home at the lake has a 1000 gallon concrete tank. Two adults with occasional family overnight visitors add waste to the system. Normal pump out over the years has been every seven to ten years. Same type of usage to this system before we purchased it. About seventy years on the system to date. No relevant issues.
Lakeside