A centrifuge for washing magnetic beads in a reaction vessel unit that includes at least one opening, having a housing including an inner surface and a drain, a rotor disposed within the housing, the rotor being configured to hold a reaction vessel unit with its opening(s) directed outwardly toward the inner surface of the housing, a motor coupled with the rotor to rotate around a horizontal rotation axis, and a magnetic element arranged in the rotor to apply a magnetic field to one or more reaction vessels of a reaction vessel unit held by the rotor.