The propeller like follower when functioning creates a pressure drop which is also in detail a partial vacuum. The distinction in air force, forces the air in the intake dock into the cleaner where the force is lower, therefore the suction effect.
The vacuum cleaner uses the physics of drag forces to trap dirt and redundant particles. The process of entrainment is created because of drag forces acting on the dirt particles. Dust entrainment works best in fast going air which is why a little intake dock cleans better than a large one.