This specification discloses vacuum cleaning apparatus for a rotary drum filter in which a drive screw for moving the suction nozzle axially of the rotary drum is supported by two movable bearings in addition to end bearings. The movable bearings are positioned on guide members which extend parallel to the drive screw to support the drive screw against sagging at locations between the suction nozzle and the end bearings. The movable bearing are spaced by rigid connecting rods. As one movable bearing is pushed along the guide member by the advancing suction nozzle, the rods pull the other movable bearing along to support the drive screw.