Abstract: Aspirator apparatus including a jar and a bung for closing the mouth of the jar, the bung comprising a domed thermoplastic top provided with a peripheral skirt within the jar mouth and having an annular slot housing an O-ring providing a primary seal with the jar, the thermoplastic material of the bung being resilient to permit depression of the domed top with reduced pressure in the jar with resulting expansion of the skirt to provide a secondary seal between the inner end of the skirt and the jar.