Abstract: Device for activating or inactivating a liquid pump on the basis of the electrical conductivity of a liquid. Device comprises, in combination, a housing having a passageway through which a liquid can flow, a pair of conductivity-sensing electrodes disposed near or in the passageway, means for connecting the passageway to a liquid pump, and means for connecting the electrodes to a conductivity-dependent pump activator connected to the pump. Device provides through-the-probe pumping and is adaptable for manual operation or in-line liquid control.