of screw described hereinafter even when the longitudinal position of screw 42 is adjusted within screw housing 40 as described hereinafter means 56 for adjusting the longitudinal position of screw 42 within screw housing 40 adjusts the position of the screw flights relative to material inlet means 22 and material outlet means 30 which are in fixed position on screw housing 40 the amount of adjustment is limited so that material inlet means 22 will always feed to a constant depth portion of screw flight means 34 for rotating screw 42 relative to screw housing 40 shown here as drive motor 34 is preferably adjustable by system control means 36 so that rpm of screw 42 can be varied and once adjusted it must hold constant so that a steady amount of material is transported from inlet to outlet and into receptacle 32 suitable means 34 includes a variable speed motor coupled to the screw shaft such that the motor has sufficient power to turn the screw at suitable rpm coupling of rotating means 34 to the shaft must be able to accommodate the longitudinal adjustment of screw 42 screw 42 is mounted within housing such that the ends of screw 42 or a shaft that is supporting screw 42 form a seal with the respective ends of screw housing 42 such that if material inlet means 22 and material outlet means 30 are also sealed none of the material that may enter the cavity will be able to exit the cavity other than through material outlet means 30 close tolerances between the shaft ends and the respective portions of screw housing 40 can.