Septic tanks need to be pumped out to remove the solid sludge that accumulates at the bottom of the tank and the grease that accumulates as scum floating near the top. Both sludge and scum can affect how well your treatment system works. How often to pump out your tank is dependant upon your tank size, the number of people residing there, and how much of your wastewater is solid waste. However, a basic rule of thumb is to have your tank pumped out approximately every 3 years.
When a system is not pumped out frequently enough, the lifespan of that system will be decreased, causing costly future repairs.