The present disclosure relates to a modular fluid pump system for configuring a fluid pump in a selected one of first and second configurations. The system may have a first pump casing with a first diameter, and a second pump casing with a second diameter smaller than the first diameter. A tubular frame may be included along with a first float having a first diameter positioned over the tubular frame for sliding longitudinal movement along the tubular frame. The first pump casing may be used to configure the fluid pump in the first configuration, to thus provide a first degree of clearance between the first float and an inner surface of the first pump casing, or alternatively the second pump casing may be used to configure the fluid pump in the second configuration, which provides a second degree of clearance between the first float and an inner of the second pump casing.