The technique of incision and drainage (I&D) is a simple but important treatment in the provision of care for abscesses. The goal of the I&D is to convert an enclosed lesion (generally a cyst or abscess) into an open one. This allows necrotic and infected material within the lesion to be removed from the body, and allows normal healing processes to resume.
I&D is generally quick, relatively painless (even without anesthesia), and simple enough for most health care providers to easily master. The offending lesion is located, the area where it is closest to the surface is defined, nearby delicate or easily-damaged tissues (such as nerves and arteries) are isolated and avoided, and a quick, short incisoin is made deep enough to pierce the fluctuant portion of the lesion.
Once I&D's, the cavity is generally probed to rule out loculated collections of material. Depending on the size of the collection, the incision could be kept open using a drain of rubber, or of some absorbant material that will act as a wick to draw out any exuded material. If the intention is to allow extended drainage for over twenty-four hours, the incision can be made in a cross or "X" shape, or a plug of skin (or mucosa) can be removed to leave an open tract into the cavity allowing further drainage. The body generally heals these larger cavities from the bottom up, filling in the cavity incrementally.
(This is not something I would wish on anyone.)
Based on my personal training, knowledge, and experience