An apparatus for flattening a flexible tube sidewall comprises a frame, a gripping roller and a handle. The frame includes a central portion extending transversely between first and second end walls. A first brake element is formed on an inner face of one wall. The roller is rotatably mounted to the walls and includes first and second ends and a cylindrical surface disposed parallel to the frame central portion to define a transverse slot. The roller end adjacent to the first brake element includes a second brake element that is engageable therewith to resist relative rotation between the roller and frame. The handle extends from the roller through the end wall for manually rotating the roller relative to the frame and drawing the tube through the slot. The brake elements cooperate to resist retrogressive movement of the tube through the slot when the handle is released.