LEACHING CHAMBER WITH INWARD FLARING SIDEWALL PERFORATIONS

摘要

A leaching chamber (20) has sidewall perforations (30) which slope downwardly from the interior to the exterior of the chamber, and which flare inwardly, so that the smallest perforation dimension is on the exterior surface of the sidewall (40). Mold cores (200) having inwardly retracting slides are used to form the chamber. Thus, perforations (30) are present down near the base flange (26) of the sidewall (40), even though the base flange has an upwardly extending fin (27).