Air is being pushed through a used oil filter to force the oil trapped in the pleated media to move. Since the filter is already saturated, the air displaces the oil and sends it out through the pleats, creating visible bubbles and flow. This turns an internal process into something you can actually see. As the air moves through the cartridge, oil exits across the surface of the filter rather than from a single point. That even movement shows how the pleats create multiple flow paths and maximiz