Abstract: A fuel tank assembly is provided. The fuel tank assembly includes a plastic fuel tank having a wall defining an outer surface and an interior volume for storing fuel therein. A portion of the fuel tank wall further defines a generally cylindrical opening therethrough. The fuel tank assembly also includes an instrument having a generally cylindrical piece extending through the opening in the fuel tank wall such that the instrument communicates with the interior volume of the fuel tank. A retainer assembly is attached to the outer surface of the fuel tank wall for releasably securing the instrument to the fuel tank. The retainer assembly includes a plastic ring-like member having a generally cylindrical inner wall disposed around the generally cylindrical piece of the instrument, the inner wall defining a circumferentially extending sealing surface. The retainer assembly also includes a reinforcing member carried within the ring-like member adjacent to and generally concentric with the sealing surface.