Delivering a blood processing solution to blood in a blood bag includes coupling a first tube to a vented spike at one end and to a Y-shaped tube connector at a second end. An in-line microbiotic barrier filter is coupled to the first tube between its ends. A second tube is coupled to a transfer bag at one end and to the Y-shaped tube connector at its other end. A third tube is coupled to the output of the Y-shaped tube connector and sealed at its distal end. The blood bag includes a fourth tube that is sealed at a distal end. The third tube is welded to the fourth tube using a sterile tubing welder, wherein a functionally-closed, sterile flow path through which the blood processing solution can flow into the blood bag is maintained.