An in-tank fuel pump assembly and mounting system is disclosed which may be configured for mounting inside a fuel tank. The assembly includes a pump housing, pump mounted to the housing, and pressure relief valve. The housing may comprise upper and lower pump housing units coupled together. The upper housing unit is configured for mounting to a tank opening, which in one implementation may be the fuel fill opening. The lower housing unit extends into the tank to approximately the bottom of the tank. A fuel fill fluid pathway is created through the housing for adding fuel to the tank while the pump assembly remains in situ. The upper housing unit may include a removable fuel cap. The pump is capable of pressurizing the fuel to pressures suitable for use in fuel injection type engines. A resiliently deformable in-tank fuel filter may be coupled to the pump.