A multi-function valve apparatus for use with a Probe-In-Loop (PIL) architecture sample injection assembly which enables both Partial-Fill and Complete-Fill injections. The rotor element is rotatable about a rotation axis relative the stator between: a Load Position, an Overfill Position, and an Injection Position. In the Load Position, a first bridge channel fluidly couples a metering syringe to the sample loop assembly enabling the probe to aspirate one of a discrete volume of sample into the probe, during a Partial-Fill Mode, and a second volume of sample into the probe, during a Complete-Fill Mode. In the Overfill Position, in the Complete-Fill Mode, a second bridge channel fluidly couples a downstream loop portion to a waste port, and the first bridge channel fluidly couples the metering syringe to an upstream loop portion of the sample loop assembly. This enables the metering pump to dispense the sample from the probe into the downstream loop portion and out the waste port to completely fill the downstream loop portion and the second bridge channel with a substantially precise known volume. In the Injection Position, the second bridge channel fluidly couples the downstream loop portion to the analyzing device to inject the sample into the analyzing device, in either the Partial-Fill Mode or and the Complete-Fill Mode.