Bung

A bung is an apparatus used to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal. The lids for safety overpacks for 55 gallon drums some times may have a bung built in[1] for access of the contents of the container. These may be referred to as fuel bungs.