Conventional septic systems are not entirely care free. The undigested solids (sludge) in the bottom of the septic tank should be pumped out every two to four years, depending on usage and tank size. If the sludge is not removed periodically, it will eventually carry over into the leach field and cause the field to fail.
A well designed system can handle a reasonable amount of normal household chemicals such as drain cleaners, laundry detergent and bleach; excessive usage can be detrimental. You should avoid putting in chemicals that are toxic to the bacteria, such as paint thinner, solvents, insecticides, etc. Cooking fats and grease should also be avoided. If a garbage disposal is used, more frequent tank pumping may be needed.
Depending on the size of the tank and your location, plan on a cost of about $200 each time the tank is pumped. When the tank is pumped, your service person should also check the tank baffles for possible damage; ask them to do this inspection before you contract with them. While the tank is open, the service technician can also run some water from a hose into the distribution box to get an indication that the leach field is also still functioning; ask if the company offers this service.