Systems and methods for processing a fluid including a suspension of biological cellular components are disclosed including a single-use kit comprising a container for the fluid a separation device for retaining selected biological cellular components and allowing other biological cellular components of said fluid to pass therethrough a flow path connecting the container to the separation device, the container being configured, when in use, to be positioned so that gravity tends to flow fluid through the flow path. The flow path has a segment in close proximity to the container with a configuration including a positive slope, so that biological cellular components moving through the segment are subjected to a gravitational force tending to impede movement through the flow path segment. The flow path segment preferably has a generally circular configuration, and a diameter of approximately 1.5 inches. Alternatively, the flow path segment may have a generally S-shaped configuration.
