Today in 1935, US Patent 2006940 A was issued, an invention of Henry H. Brockmeyer, for his “Bung and a Method of Making Bungs.” There’s no Abstract, although in the description it includes this summary:

The invention relates to means particularly adapted to prevent seepage of liquids through bung and in many instances, especially for the reason that presently bungs usually are constructed from wood derived from relatively small trees, the grain does not extend parallel with the inner and outer surfaces of the bung but curves inwardly or outwardly whereby the liquid, particularly beer, which is under relatively heavy pressure within the container, is adapted to seep through the pores in the wood of the bung, or through the channels adjacent the grain. Moreover, the pressure of air or gases within the container is reduced as by escape of such air or gases through the pores or channels, in the bung, adjacent the grain, simultaneously when the liquid within the container seeps therethrough. Since it is advantageous to retain the air or gas pressure within the container, as well as prevent seepage of the liquid from within said container outwardly through the bung, any leakage of air or seepage of liquid is undesirable.

Therefore, an important object of the invention is to provide simple, efficient, practical and economical means to prevent passage of air or gases through a bung and to prevent seepage of liquid through said bung.

Other objects of the invention are to provide dependable means adapted to render the inner surface of a bung impervious to liquids, such as beer, whiskey, and the like; and to provide means which is unlikely to interfere or retard natural expansion of said bung, when contacted by said liquid, for the purpose of sealing the bung hole in which said bung is positioned.