A method for washing biological cells comprising: providing a separator (10, 301) comprising a relatively rotatable cylindrical housing and an internal member; wherein said cylindrical housing has an interior surface and said internal member has an exterior surface, said surfaces defining a gap therebetween, wherein at least one of said surfaces includes a porous membrane; introducing cells suspended in a liquid medium into said gap; rotating at least one or both of said housing and said internal member; separating said cells from said liquid medium; concentrating said cells; removing at least some of said concentrated cells from said separator (10, 301) through a first outlet to a first integrally connected in-process container; removing at least some of said separated liquid medium from said separator through a second outlet; introducing replacement fluid into said first integrally connected in-process container to resuspend the concentrated cells therein; introducing said resuspended cells into said gap of said separator and separating the resuspended cells from the replacement fluid; concentrating said cells and removing said concentrated resuspended cells from said separator (10, 301) through the first outlet to a second integrally connected in-process container; removing at least some of the separated replacement fluid from said separator through said second outlet; measuring and recording the volume or weight of concentrated resuspended cells in said second integrally connected in-process container; and filling a final product container upon reaching an acceptable level of the concentration of the cells to replacement fluid. providing a separator (10, 301) comprising a relatively rotatable cylindrical housing and an internal member; wherein said cylindrical housing has an interior surface and said internal member has an exterior surface, said surfaces defining a gap therebetween, wherein at least one of said surfaces includes a porous membrane; introducing cells suspended in a liquid medium into said gap; rotating at least one or both of said housing and said internal member; separating said cells from said liquid medium; concentrating said cells; removing at least some of said concentrated cells from said separator (10, 301) through a first outlet to a first integrally connected in-process container; removing at least some of said separated liquid medium from said separator through a second outlet; introducing replacement fluid into said first integrally connected in-process container to resuspend the concentrated cells therein; introducing said resuspended cells into said gap of said separator and separating the resuspended cells from the replacement fluid; concentrating said cells and removing said concentrated resuspended cells from said separator (10, 301) through the first outlet to a second integrally connected in-process container; removing at least some of the separated replacement fluid from said separator through said second outlet; measuring and recording the volume or weight of concentrated resuspended cells in said second integrally connected in-process container; and filling a final product container upon reaching an acceptable level of the concentration of the cells to replacement fluid.