A modular fluid pump system for configuring a fluid pump in a selected one of first and second configurations, the system comprising: a first pump casing having a first diameter; a second pump casing having a second diameter smaller than the first diameter of the first pump casing; a tubular frame; a first float having a first diameter a second float having a second diameter smaller than the first diameter of the first float an upper support ring coupled to an upper end of the tubular frame; a lower support ring coupled to a lower end of the tubular frame; an inlet operatively coupled to the lower support ring; and wherein either: to configure the fluid pump in the first configuration, the first float is positioned over the tubular frame for sliding longitudinal movement along the tubular frame, and the first pump casing is operatively coupled to the tubular frame, to thus provide a first degree of clearance between the first float and an inner surface of the first pump casing; or to configure the fluid pump in the second configuration, the second float is positioned over the tubular frame for sliding longitudinal movement along the tubular frame, and the second pump casing is operatively coupled to upper and lower support rings (38, 48), to thus provide a second degree of clearance between the second float and the inner surface of the second pump casing, wherein the second degree of clearance is less than the first degree of clearance. a first pump casing having a first diameter; a second pump casing having a second diameter smaller than the first diameter of the first pump casing; a tubular frame; a first float having a first diameter a second float having a second diameter smaller than the first diameter of the first float an upper support ring coupled to an upper end of the tubular frame; a lower support ring coupled to a lower end of the tubular frame; an inlet operatively coupled to the lower support ring; and wherein either: to configure the fluid pump in the first configuration, the first float is positioned over the tubular frame for sliding longitudinal movement along the tubular frame, and the first pump casing is operatively coupled to the tubular frame, to thus provide a first degree of clearance between the first float and an inner surface of the first pump casing; or to configure the fluid pump in the second configuration, the second float is positioned over the tubular frame for sliding longitudinal movement along the tubular frame, and the second pump casing is operatively coupled to upper and lower support rings (38, 48), to thus provide a second degree of clearance between the second float and the inner surface of the second pump casing, wherein the second degree of clearance is less than the first degree of clearance. to configure the fluid pump in the first configuration, the first float is positioned over the tubular frame for sliding longitudinal movement along the tubular frame, and the first pump casing is operatively coupled to the tubular frame, to thus provide a first degree of clearance between the first float and an inner surface of the first pump casing; or to configure the fluid pump in the second configuration, the second float is positioned over the tubular frame for sliding longitudinal movement along the tubular frame, and the second pump casing is operatively coupled to upper and lower support rings (38, 48), to thus provide a second degree of clearance between the second float and the inner surface of the second pump casing, wherein the second degree of clearance is less than the first degree of clearance.