As the septic tank is used, sludge accumulates at the bottom and scum at the top of your septic tank. When the sludge + scum levels increase beyond 25-33% of the total tank capacity, 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.