this invention relates to the manufacture of flexible porous plastic irrigation and aeration pipe having an essentially uniform porosity throughout its length . the process for making the porous pipe includes volumetrically delivering to a mixing hopper for preblending thermoset polymer particles and a thermoplastic binder for the particles , preblending the components in the hopper , volumetrically feeding from the hopper the preblended components for controlled discharge into an extruder , and extruding the preblended components to produce the porous plastic pipe .