A mechanism for use with an anchoring structure of a drainage catheter. A suture thread as a flexible link extends from the distal end of a catheter through the catheter lumen to the mechanism at the proximal end of the catheter. The mechanism includes a distal body affixed to the proximal end of the catheter and a proximal body that can be displaced axially with respect to the distal body between clamping and unclamped positions. In a clamped position, the bodies clamp the suture thread to prevent inadvertent displacement of the suture thread. Displacement of the proximal body in certain embodiments takes up slack in the suture thread generated when the anchor forms.