A frangible or breakaway valve for use in a flexible tube. The valve comprises two parts: a tubular portion with a closed end and an elongated, generally rigid handle breakably attached to the closed end. The elongated handle has projections which frictionally contact the interior surface of the flexible tube and prevent the elongated handle from moving back into a closed position once the elongated handle has been broken. The valve may be used in conjunction with tubing and a plastic container of dialysis solution. The valve is opened by breaking away the elongated, generally rigid handle and moving "walking" the rigid handle down the tube by folding the tube back and forth upon itself. The projections on the rigid breakaway handle have sufficient frictional contact with the inside of the tube to assure that the handle will not move back into contact with the tubular portion, and the valve will remain open.