Abstract: Dialysate preparation apparatus having a main flow line having one end for connection to a source of water and another end for providing dialysate to a dialyzer, a concentrate flow line having one end connected to a junction on the main flow line and another end with a connector for alternatively connecting the concentrate line to a source of dialysate concentrate or a source of cleaning fluid, a source of dialysate connectable to the connector, a source of cleaning fluid having a cleaning fluid flow line with an end that is connectable to the connector, a flow sensing switch on the cleaning fluid flow line, and a controller connected to receive a signal from the switch to verify that the apparatus is in a cleaning mode when the switch indicates fluid flowing in the flow line. Also disclosed is a controller providing an initial backflush prior to pumping cleaning fluid into the apparatus in order to provide a water interface between the dialysate and the incoming cleaning fluid.