Final answer:
Before a flexible sigmoidoscopy, a patient will self-administer an enema, which is in liquid form, to clear the sigmoid colon for better visibility during the examination.
Step-by-step explanation:
The enema that a patient self-administers at home before a flexible sigmoidoscopy is in liquid form. This preparation helps to clear the large intestine, specifically the sigmoid colon, to allow for better visibility during the procedure. Enemas work by introducing a fluid into the rectum and lower bowel to trigger the bowel to expel its contents, which is essential before a sigmoidoscopy to ensure that the doctor has a clear view of the bowel lining.