Septic systems should be inspected and pumped a minimum of once every three to four years. You may not be experiencing any problems now, but a full septic tank may allow unwanted solids to flow into the drain field, which is the part of the system that consists of a distribution box, with a series of connected pipes. Each pipe allows water to flow into a bed of stone that drains into the ground. If paper and other solids flow into the drain field it becomes blocked and ineffective. A blocked drain field is costly to repair or replace.