Anal glands are located at the 5&7 or 4&8 o'clock positions around the anus, depending on which book you read. They sit inside the skin between the outer layer of the skin and the inner layer of muscle of the rectum. They must be expressed regularly or they can build up and become infected or even abscess. The regular color for anal glands fluid is kind of brown and smelly.

Locations (drawn to where they would theoretically be if we could see inside the dog)

An abscess from a poor pup who didn't get to express his anal glands (due to tapeworms, poor diet, etc)