A rotary agitator for use in sealed containers such as drums having a single bung opening. The agitator is provided with a housing which screws into the bung opening and appending from the housing is a rotating hollow shaft having a helical agitator flight or other agitator member which may be inserted through the bung opening. Material from inside the drum or container may be withdrawn upwardly through the hollow shaft and then outwardly through a port in the housing. A check valve is provided in the housing which communicates with the interior of the container in which to allow pressure equalization in the container which may be connected to a source of inert gas or the like to prevent degradation or other harm to the material in the drum which might be caused by ambient atmosphere.