Septic systems are designed to keep solids in the tank and allow effluent (liquid) to leave. When too many solids are in the tank, it can get out to your drainfield and clog up the lines and rock-bed.
We recommend pumping every 3-5 years. This number can vary depending on how many people are in the home, the size of the tank, and what you put down the drain. Have an O&M inspection annually to make sure you are pumping out your tank before it leads