A device for cleaning a duct comprises a rotating whip head, the filaments of which flail the interior of the duct as the head is moved lengthwise by a flexible shaft comprised of segments which are attached to each other by disengageable two-part couplings. Proximal and distal ends of a whip head, and the proximal ends of coupling parts are provided with rake features that provide inclined plane surfaces, enabling the rotating devices to avoid hanging up on steps and edges within the duct.