As the septic tank is used, sludge continues to accumulate in the bottom of the septic tank. Generally speaking, properly designed tanks have enough space for three to five years safe accumulation of sludge. When the sludge level increases beyond this point, sewage has less time to settle properly before leaving the tank. As the sludge level increases, more solids escape into the filter bed or leach bed area. If sludge accumulates too long, no settling occurs before the sewage escapes directly to the absorption area. When this happens your system will become faulty and needs to be replaced. To prevent this, the tank must be pumped out periodically.