Abstract: Rotatable fill pipe for use in blind-filling underground voids has a collapsible backfill elbow on the lower end thereof, including an upper elbow part rigidly connected to the lower end of the fill pipe and a lower elbow part pivotally connected to the upper elbow part for pivotal movement between a lower position in coaxial alignment with the fill pipe to facilitate passage of the backfill elbow and lower end of the fill pipe through a fill hole into an underground void, and a raised position extending at an angle relative to the fill pipe to facilitate distribution of fill material introduced into the underground void through the fill pipe in a circular pile within the underground void as the fill pipe and backfill elbow are rotated about the longitudinal axis of the fill pipe. A cable may be connected to the lower elbow part for remotely actuating the lower elbow part for pivotal movement between the lower and raised positions.