A self-venting trashcan system for use with a trashcan having interior smooth sides and a bottom interior surface has an extruded rigid polymeric strip with an adjustable bend formed on its left and right sides bendable along a thin web for contacting smooth sidewalls of a trashcan. Along its height and perpendicular thereto a plurality of parallel easy-to-fracture lines are provided. The user breaks the polymeric strip to thereby adjust its height to be shorter than the height of the trashcan. The left and right sides of the polymeric strip are attached to the smooth sidewalls of the trashcan by double-sided pressure sensitive adhesive tape, leaving a gap or air entry/exit between the top and bottom of the polymeric strip and the top and bottom surface of the trashcan, respectively. During trashcan liner placement, air pockets are smoothed out. Air moves freely in both directions, entering/exiting, between the polymeric strip and the trashcan, and the trash filled plastic liner is readily removed without tearing or vacuum pull-back.