A method for draining a culture from a container assembly, the method comprising: tilting an elongated support housing having a longitudinal axis that extends along the length thereof, the support housing having a chamber that is partially bounded by a floor, a container assembly being disposed within the chamber of the support housing so as to rest on the floor, the container assembly comprising a flexible bag bounding a compartment in which a fluid is disposed, the fluid comprising a medium and also cells or microorganisms, the support housing being tilted from a first position wherein the longitudinal axis is vertically oriented to a second position wherein the longitudinal axis is in a range between 2° and 45° from vertical with between 5° and 25° from vertical being more common; and opening a valve so that when the support housing is in the second position, at least a portion of the fluid within the flexible bag flows out of the bag through a drain line that is coupled with the bag; characterized by repeatedly rocking the support housing and the container assembly disposed therein relative to a stand on which the support housing is pivotably mounted so as to mix the fluid within the container assembly prior to the step of tilting support housing to the second position for removing the fluid, wherein the repeatedly rocking comprises repeatedly moving the support housing between: a forward tilt position wherein the longitudinal axis is tilted forward at least 5° from vertical; and a rearward tilt position wherein the support housing is tilted in a direction opposite the forward tilt position so that the longitudinal axis is tilted rearward at least 5° from vertical. tilting an elongated support housing having a longitudinal axis that extends along the length thereof, the support housing having a chamber that is partially bounded by a floor, a container assembly being disposed within the chamber of the support housing so as to rest on the floor, the container assembly comprising a flexible bag bounding a compartment in which a fluid is disposed, the fluid comprising a medium and also cells or microorganisms, the support housing being tilted from a first position wherein the longitudinal axis is vertically oriented to a second position wherein the longitudinal axis is in a range between 2° and 45° from vertical with between 5° and 25° from vertical being more common; and opening a valve so that when the support housing is in the second position, at least a portion of the fluid within the flexible bag flows out of the bag through a drain line that is coupled with the bag; characterized by repeatedly rocking the support housing and the container assembly disposed therein relative to a stand on which the support housing is pivotably mounted so as to mix the fluid within the container assembly prior to the step of tilting support housing to the second position for removing the fluid, wherein the repeatedly rocking comprises repeatedly moving the support housing between: a forward tilt position wherein the longitudinal axis is tilted forward at least 5° from vertical; and a rearward tilt position wherein the support housing is tilted in a direction opposite the forward tilt position so that the longitudinal axis is tilted rearward at least 5° from vertical. a forward tilt position wherein the longitudinal axis is tilted forward at least 5° from vertical; and a rearward tilt position wherein the support housing is tilted in a direction opposite the forward tilt position so that the longitudinal axis is tilted rearward at least 5° from vertical.