A plug which has a plugging portion and a stem extending therefrom is formed of an elastomeric material in order to deform to create a wiping engagement and a seal with the walls of a receiving cavity. The stem and plugging portion include both cavities for receiving alignment pins in the device being plugged and a manually engageable portion on a distal end of the stem for removing the plug from the sealed cavity, such as within an optical subassembly module. The side edges of the plugging member conform to the cavity cross-section to enhance the sealing yet do not unduly deform the member. The sealing member is formed with one or more standoffs to engage an end face of the cavity, assuring no contact between the optical elements and the plug. The edges of the plug deform upon insertion to create the seal and form a wiping engagement with the cavity interior.