Keep in mind that a septic system costs less than $300 to pump but $12,000 or more to replace and can affect the resale of your property. If your system shows signs of failure, is in coarse, sandy soils, or is within 100 feet if a lakeshore or stream, plan to replace it. septic system is a sewage treatment and disposal system buried in the ground. It is composed of a septic tank and a leach field or trench. Household sewage (wastewater from sinks, toilets, showers, washing machines, garbage disposals and dishwashers) generally flows by gravity into the septic tank.