A testing method includes the steps of: (1) providing a negative pressure generator; (2) generating a negative pressure in a fluid passageway and a chamber which are in fluid communication with a guiding section of a fluid reservoir wherein a second sensing element is affixed to a guiding section of the fluid reservoir; (3) transferring a fluid flow stream from the guiding section to the chamber via the fluid passageway and drawing a float having a first sensing element from an upper position to a lower position within the guiding section; (4) generating a signal via the first and second sensing elements as the float moves relative to the second sensing element within the guiding section; and (5) transmitting a signal to at least one of a control unit or a graphical user display.