A pump mount base for a filter/pump assembly in a pool or spa fluid handling system allows a user to adjust the height of the filter/pump assembly and thus its fluid inlets and fluid outlets. This adjustability allows the user to choose from a variety of replacement assemblies rather than being forced to select the same filter/pump assembly previously or originally used in the system. The height of the filter/pump assembly may be further altered by the engagement of shims, which may be positioned by pins in the bottom surface of the shim that engage corresponding apertures formed in an upper support surface of the pump mount base. The shims may be formed integrally with the pump mount base in the molding process by which the base is formed, and/or the shims may be provided separately.