What can cure a sore rectum?

Sore rectum. There are many different causes of a sore rectum (proctitis, infection, diarrhea, inflammatory bowel disease, etc.), but the most common is hemorrhoids. The best initial treatment, regardless of cause is just to sit in a hot tub for 20 minutes or so several times a day. An anti-inflammatory medicination like Ibuprofen will help. If symptoms persist, see your doctor.
Depends. First one has to determine why the rectum is sore. A fissure, hemorrhoids, abscess are all possibilities as well as a tumor, so proper diagnosis will determine the best form of treatment.