Soakaway
The soakaway is a pit for collecting the liquid effluent from a septic tank.
which is then allowed to infiltrate the ground
The capacity of the pit should be at least equal to that of the septic tank
The pit may be filled with stones, broken bricks, etc., in which case no lining is need, or it may be lined with open jointed masonry (often with a filling of sand or gravel between the lining and the soil to improve infiltration).