A 40-year-old man presents to the emergency department 4 days after band ligation of a grade 2 internal hemorrhoid with a fever and reports of urinary retention. On evaluation, vital signs indicate temperature 102.2 °F, heart rate of 102 beats per minute, and blood pressure of 114/80 mmHg. Laboratory evaluation is significant for a white blood cell count of 17,000. Physical examination reveals significant anorectal tenderness and swelling. Based on these findings, the best next step in management is