A 50-year-old man undergoes low anterior resection for rectal cancer. Five days later he developed focal pelvic discomfort without generalized abdominal pain, fevers of 102 °C, and a leukocytosis count of 18,000. His blood pressure is 118/72 mmHg and his heart rate is 112. Computed tomography (CT) with rectal contrast confirms an anastomotic leak with a 6-cm abscess with contrast extravasation. What is the best next step?