Note- 36" HDPE pipe will not nest into 42" pipe; 42" HDPE pipe will not nest into 48" pipe.

Class 1 Perforations (uncommon)
The rows of perforations shall be arranged in two equal groups placed symmetrically on either side of the lower side of the unperforated pipe below the spring line on the outside valleys of the corrugations.
Intended use, subsurface drainage or combination storm and under drain.

Class 2 Perforations (common)
The rows of perforations are evenly spaced for each diameter around the entire circumference on the outside valleys of the corrugations.
Intended use, subsurface drainage only.