Trace the sensor wires on the side of the tank to the sensor. Take off the wires with a wrench by removing the nut holding them in place.
Pull the wires out of the old sensor and remove the sensor by unscrewing it out from the rub grommet. Push the rubber grommet into the tank and insert the new one into the hole.
Place the new sensor in the same spot and screw into the tank through the grommet. Attach the wires to the sensor and secure in place with the retaining nut.