Complex sentence: The glands can be emptied by the dog's keeper, or more typically by a groomer or veterinarian, by squeezing the gland so the contents are released through the small openings on either side of the anus.
Split into simpler sentences: The glands can be emptied by the dog's keeper, or more typically by a groomer or veterinarian. A dog groomer addresses this need by squeezing the gland so the contents are released through the small openings on either side of the anus.