A method of separating blood into two or more components and washing a component, comprising: providing a blood storage container containing an initial blood composition; providing a blood separation circuit comprising a separator (10, 108) including a pair of relatively rotating surfaces spaced apart to define a gap therebetween, at least one of the surfaces comprising a membrane that allows non-cellular material to pass therethrough and substantially prevents the passing of cellular material; priming the blood separation circuit with at least one of a blood cell preservative, additive solution, wash media, and the initial blood composition; flowing the initial blood composition from the blood storage container through the gap, to allow substantially all of the non-cellular material to pass through the membrane but not all of cellular material; withdrawing cellular material from the gap to a RBC container and retaining the cellular material in the RBC container; flowing a first portion of additive solution from an additive solution container (76a, 102) through the gap, withdrawing at least some of the first portion of additive solution from the gap and retaining it in the RBC container to produce a first mixture; flowing a second portion of additive solution from the additive solution container (76a, 102) through the gap, withdrawing at least some of the second portion of additive solution from the gap and retaining it in the blood storage container; flowing at least a part of the first mixture from the RBC container to the additive solution container (76a, 102) to produce a second mixture; flowing at least a part of the second mixture from the additive solution container (76a, 102) through the gap; flowing a supernatant of the second mixture to a wash media bag, the supernatant of the second mixture comprising primarily non-cellular material and/or additive solution that has crossed the membrane, and flowing a remaining portion of the second mixture comprising substantially of purified cellular material from the gap to the RBC container; and flowing at least part of the second portion of additive solution from the blood storage container through the gap, withdrawing at least a part of the second portion from the gap and retaining at least part of the second portion in the RBC container. providing a blood storage container containing an initial blood composition; providing a blood separation circuit comprising a separator (10, 108) including a pair of relatively rotating surfaces spaced apart to define a gap therebetween, at least one of the surfaces comprising a membrane that allows non-cellular material to pass therethrough and substantially prevents the passing of cellular material; priming the blood separation circuit with at least one of a blood cell preservative, additive solution, wash media, and the initial blood composition; flowing the initial blood composition from the blood storage container through the gap, to allow substantially all of the non-cellular material to pass through the membrane but not all of cellular material; withdrawing cellular material from the gap to a RBC container and retaining the cellular material in the RBC container; flowing a first portion of additive solution from an additive solution container (76a, 102) through the gap, withdrawing at least some of the first portion of additive solution from the gap and retaining it in the RBC container to produce a first mixture; flowing a second portion of additive solution from the additive solution container (76a, 102) through the gap, withdrawing at least some of the second portion of additive solution from the gap and retaining it in the blood storage container; flowing at least a part of the first mixture from the RBC container to the additive solution container (76a, 102) to produce a second mixture; flowing at least a part of the second mixture from the additive solution container (76a, 102) through the gap; flowing a supernatant of the second mixture to a wash media bag, the supernatant of the second mixture comprising primarily non-cellular material and/or additive solution that has crossed the membrane, and flowing a remaining portion of the second mixture comprising substantially of purified cellular material from the gap to the RBC container; and flowing at least part of the second portion of additive solution from the blood storage container through the gap, withdrawing at least a part of the second portion from the gap and retaining at least part of the second portion in the RBC container.