A mixing system is disclosed in which the system comprises a source of bone-graft or bone-graft-substitute material, a liquid source, and a vacuum source, at least one of the source of bone-graft or bone-graft-substitute material and the liquid source being in communication with the vacuum source. A valve assembly also forms part of the system, the valve assembly having a valve movable between a first position in which a first fluid passageway is created between the source of bone-graft or bone-graft-substitute material and the vacuum, and a second position in which a second fluid passageway is created between the source of bone-graft or bone-graft-substitute material and the liquid source, wherein, in the second position, the valve seals off the first fluid passageway, the vacuum source being adapted to generate a negative-pressure environment, relative to atmospheric pressure, within the valve assembly while the valve is in the first position. Methods of utilizing the aforementioned system are also disclosed.