A user-supplied cordless drill spins a flexible cable within a nylon sheath while a chain knocker expands to the pipe's inner diameter to break blockages and clean walls; carbide-tipped knockers are available for scale and light roots, and plain chains for general grease and soft blockages. The system is lightweight and works well with inspection cameras during cleaning.

It is not recommended to clean glass, ceramic, porcelain, or similar fixtures with FlexShaft drain cleaners as they may be damaged.

Use a cordless drill with 1800–2500 RPM, 3/8" (10 mm) or greater chuck, adjustable clutch, momentary contact switch, and no switch lock. Do not use corded drills, hammer drills, or impact drivers. Set the drill in screw driving mode so the clutch functions, and begin with a low clutch setting around 25% of the range.

Operate in a clear, level, stable, dry location and do not stand in water. Inspect the drain, identify access points, pipe sizes, materials, and blockages; remove fixtures if needed and avoid running the knocker in fixtures. Position the cable outlet within 3' (1 m) of the drain inlet, and have water flowing during cleaning to wash debris away.

Select the correct knocker for pipe size and application, ensure proper setup and adjustment, and begin with conservative clutch settings. Keep at least 1' (0.3 m) of knocker inside the drain before rotation and avoid forcing the knocker into blockages; increase clutch setting as needed up to about 75% if it continues to slip.