How do I know when my septic tank is full and it needs to be pumped out?

A properly functioning tank is always full. A typical septic tank has a capacity of 1000 gallons and, if working properly, will always be full. The idea
behind the septic tank is that as one gallon enters the tank from the house, one gallon leaves the tank and goes to a drain field. The 1000 gallon tank allows fats, oils and grease to float and solids to settle. A good time to pump your tank is when either of those levels exceeds 6-8 inches. The average household will accumulate these levels in 2-3 years.