Drainage is a medical or surgical procedure that involves collecting fluids or gases produced by the body, and evacuating them to the outside or to the inside of the body. This technique is often used in surgery after an operation where bleeding can continue after closing the incision: the installation of a drain will allow the blood to drain out of the body which prevents the formation of a hematoma. It is also used to drain an abscess, an infected mass in the body. During pneumothorax, a needle is placed in the pleura allow the evacuation of unwanted air. The bronchial drainage performed by a physical therapist can relieve breathing difficulties by emptying the lungs of their secretions. Lymphatic drainage can reduce or avoid the occurrence of edema. Wearing stockings is also a technique of drainage and facilitates blood circulation.