An analysis system may perform operations on an analyte that may be combined with multiple regents prior to being introduced into a flow cell. The instrument may include a volume into which the reagents to be combined with the analyte are aspirated one-by-one. The volume may be formed as a serpentine channel in a valve manifold associated with sippers for aspirating the reagents. The reagents may then be mixed by cycling a pump to move the reagents within the mixing volume or channel. For this, the reagents may be aspirated from a recipient into the volume or channel, ejected back into the recipient, and this process may be performed repeatedly to enhance mixing.