Need to drain a painful blister? To avoid infection, follow these steps: Wash your hands and the blister with soap and warm water. Swab the blister with iodine and sterilize a clean, sharp needle with rubbing alcohol. Puncture the blister at several spots along the edge. Let the blister drain, but leave the overlying skin alone. Apply an ointment (Vaseline, Plastibase, other) to the blister and cover it with a bandage. Change the dressing every day, applying more ointment and a new bandage.