Abstract: The present invention relates to an improvement for use in a device where a liquid floating on top of another liquid is to be drained to another part of the device, and where these are to be intimately mixed with each other in the form of a vortexinducing structure comprising at least one curved vane located above the exit port of the liquid, the vane extending substantially to the upper level of the liquid system, a lateral inlet being provided along a larger part of the vane structure. Preferably the device comprises a helical vane extending to the top level of the upper liquid, positioned above the outlet port.