A nozzle assembly for an injection molding system has a nozzle adapter with one or more vent holes therein. A porous metal insert is provided in fluid communication with at least one of the vent holes. The porous metal insert is also in fluid communication with a flow channel through the nozzle assembly. As molten polymeric material advances through the flow channel from a barrel to a mold assembly, gases entrained in the molten polymeric material are vented through the porous metal insert and escape through the one or more vent holes. Pressurized air may be introduced through the vent holes, such as by one or more blow-back modules, to unclog pores of the one or more porous metal inserts between shots of the injection molding system.