Inter alia, a method for mixing a first liquid with a second liquid in a pump cassette (202), characterized in that the method comprises: pumping a first liquid into a first pump chamber (334) of the pump cassette (202) through a channel (310) of the pump cassette (202), while pumping a quantity of a second liquid from a second pump chamber (333) of the pump cassette (202) into one of the channel (310) and the first pump chamber (334), so as to mix the first liquid and the second liquid within the pump cassette (202) is disclosed.An apparatus for mixing a first liquid with a second liquid is also disclosed.
