A pneumatically driven fluid pump apparatus is disclosed which includes a pump casing having an inner wall, a pump cap secured at a first end of the pump casing, and a liquid discharge tube in communication with the pump cap and extending at least partially within an interior area of the pump casing toward a second end of the pump casing, and where fluid is admitted into the pump casing at the second end. The pressurized airflow causes a swirling flow of the liquid within the interior area of the pump casing that helps to clean the interior area of the pump casing by liquid scrubbing action to dislodge debris adhered within the interior area of the pump casing and remove the debris up through the liquid discharge tube and out from the fluid pump apparatus during a liquid eject cycle.