Water Return for eBay Chinese K40 Laser

This is ~ 7mm OD with a ~3mm ID water return line with hose barb designed to a fixed to the top of five gallon bucket for the water return of a K40 style eBay/Chinese Laser cutter & engraver.  The idea is to provide a little back pressure to trigger a small pressure sensor to indicate water flow exiting the tube rather positive pressure enter it because if the becomes plugged, the inlet would show pressure activating the switch yet no water would be flowing and the tube could be damaged.