Agitator arrangement for mixing a liquid within a mixing tank and for cleaning the interior of the tank , wherein the agitator arrangement comprises: a stationary outer pipe extending in an axial direction having an upper end region configured for being fastened to the mixing tank and a lower end region configured to be located within the tank ; a rotatable inner pipe located partly within and extending coaxially with the stationary outer pipe and forming a first flow channel within the rotatable inner pipe and a second flow channel in a space between an interior surface of the stationary outer pipe and an exterior surface of the rotatable inner pipe , a rotatable outer member fastened to the rotatable inner pipe and including a cleaning unit having at least one opening for spraying a pressurized cleaning liquid supplied through the second flow channel on an interior surface of the tank , characterised in that the agitator arrangement further comprises a seal for sealing an axial gap between an axial end surface of the lower end region of the stationary outer pipe and an oppositely facing upper axial end surface of the rotatable outer member , wherein the seal has a substantially cylindrically shaped portion and a radially inwardly protruding rib located in the axial gap , and wherein the seal is configured to interact with the pressurized cleaning liquid, such that a lower sealing surface of the seal , upon flow of the pressurized cleaning liquid in the second channel to the cleaning unit , is arranged to sealingly abut the upper axial end surface of the rotatable outer member while allowing relative motion between the stationary outer pipe and the rotatable outer member in a radial direction . a stationary outer pipe extending in an axial direction having an upper end region configured for being fastened to the mixing tank and a lower end region configured to be located within the tank ; a rotatable inner pipe located partly within and extending coaxially with the stationary outer pipe and forming a first flow channel within the rotatable inner pipe and a second flow channel in a space between an interior surface of the stationary outer pipe and an exterior surface of the rotatable inner pipe , a rotatable outer member fastened to the rotatable inner pipe and including a cleaning unit having at least one opening for spraying a pressurized cleaning liquid supplied through the second flow channel on an interior surface of the tank , characterised in that the agitator arrangement further comprises a seal for sealing an axial gap between an axial end surface of the lower end region of the stationary outer pipe and an oppositely facing upper axial end surface of the rotatable outer member , wherein the seal has a substantially cylindrically shaped portion and a radially inwardly protruding rib located in the axial gap , and wherein the seal is configured to interact with the pressurized cleaning liquid, such that a lower sealing surface of the seal , upon flow of the pressurized cleaning liquid in the second channel to the cleaning unit , is arranged to sealingly abut the upper axial end surface of the rotatable outer member while allowing relative motion between the stationary outer pipe and the rotatable outer member in a radial direction . <EOS>