Technic Tube - Flexible - LEGO® Black Pneumatic Tube 600MM - 1915 - The shop Briques Passion
Quickun Pneumatic Tubing 8mm x 5mm PU Polyurethane Tube Air Hose Line for Air Compressor Fitting or Fluid Transfer (Blue 32.8ft/10Meters) - - Amazon.com
Quickun Pneumatic Tubing 6mm x 4mm PU Polyurethane Tube Air Hose Line for Air Compressor Fitting or Fluid Transfer (Black 32.8ft/10Meters) - - Amazon.com
Pneumatic Tubing : Set 970119-1 | BrickLink
Lego compatible pneumatic tube
Sheepo's Garage: Alternative parts for rare soft axles