A pigtail is a coiled or looped section of tubing used in piping and instrumentation systems to absorb vibration, manage thermal expansion, and protect pressure instruments from direct exposure to process media. Moreover, its curved design allows it to flex under temperature or pressure changes. A pigtail catheter is a small, flexible medical device used to drain unwanted fluid or air from a body cavity, most commonly the pleural space surrounding the lungs. 3 French pigtail catheter placements. Both do the same job — removing air or fluid from around the.