Embodiments of a clamp for compressing a flexible tube are disclosed herein. In one such embodiment, the clamp includes a first member, a second member moveably coupled to the first member to move into and out of a clamping position to apply a compressive force to the tube, a locking member to hold the first and second members in the clamping position, a third member moveably retained between a pair of sidewalls of one of the first member and the second member, and a fourth member moveably coupled to one of the first member and the second member and engageable with the third member to apply an additional compressive force to the tube.