A sonotrode specially adapted for defoaming liquids during container filing operations, has an upper body portion having a first diameter and having an upper face adapted to be mounted to a driving transducer, a middle body portion having a second diameter larger than the first diameter situated below the upper body portion, a generally conical portion situated between the upper body portion the middle body portion, and a transition portion situated between the middle body portion and a lower face adapted to be directed toward a liquid upper surface within a container, the lower face being generally rectangular.