A venturi eductor comprising a flow passage for a first liquid, a dispensing passage with an opening into the flow passage to allow a second liquid to be drawn therethrough and into a first liquid flowing through the flow passage, and a flow restrictor in the dispensing passage, in which the flow restrictor comprises a body with a plurality of nozzles passing therethrough with varying sizes of orifice, which body is movable between a first position in which a first of said nozzles is disposed in the path of the second liquid, and further positions in each of which a further of said nozzles is disposed in the path of the second liquid.