ADS 04150020IBDW 4" x 10' Smoothwall Pipe - Meeting ASTM F810, Smoothwall is very popular for sanitary leach field use because of its low cost, large perforations, and high beam strength when compared to singlewall perforated polyethylene pipe. Beam strength is a measure of the stiffness of a pipe in the longitudinal direction. Because Smoothwall is relatively stiff in the longitudinal direction, it can easily be laid straight and "true to line and grade." Smoothwall pipe requires a stone backfill/envelope to allow it to function effectively for leach field applications.