A method in connection with a pump drive connected to a container or the like, wherein a frequency converter is arranged to supply power to a pump in such a manner that a pump flow (Qp) is responsive to an estimated mean incoming flow (Qest) to the container. The method includes draining the container, allowing the container to fill during a predefined filling time (tfill) while the pump is inactive, draining the container again at a known pump flow (Qp,nom), defining the drainage time (tdrain), defining an estimated mean incoming flow (Qest) on the basis of the filling time (tfill), drainage time (tdrain) and known pump flow (Qp,nom), and setting the power supplied by the frequency converter to the pump to be such that the pump flow (Qp) corresponds to the produced estimated mean incoming flow (Qest).