Abstract: A dilutor has a control interface to receive control signals and a block having an orifice. The dilutor has a single piston at least partially within the block, and there is not another piston within the block. The dilutor has a motor and drive configured, in response to the control signals, to automatically move the single piston away from the orifice to aspirate fluid and to move the single piston toward the orifice to dispense the aspirated fluid. The dilutor has a first valve coupled to the orifice and configured, in response to the control signals, to automatically couple the orifice either to a sample line or to a diluent line.