Septic tanks require some extra maintenance. In spite of what you hear, have your septic tank pumped out every five years. When solids build up, the damage is not to the tank, but to the leech field. The solids become as hard as concrete when they dry out. If this happens in the leech field or the laterals, they must be dug up and replaced.
Also, you must keep bacteria alive and well in the tank. You can either buy bacteria by the box, or you can just add yeast to the tank.