Eight days after ileal-pouch anal anastomosis (IPAA) and diverting loop ileostomy, your patient presents to the emergency department with pelvic pain, low-grade fever, and purulent drainage per anus. The patient is hemodynamically stable with a white blood cell (WBC) count of 14. Intravenous (IV) antibiotics and fluids are initiated. Computed tomography (CT) with rectal contrast reveals a deep pelvic abscess with contrast extravastion into the cavity. What is the best next step in the management of this patient?