This was not on yorkies, but would be the same thing. Perhaps it will help someone.
HAPPY EXPRESSION EVERYONE!
Your dog has two anal sacs, one on each side of the anus. The sacs contain a very strong-smelling liquid that pets use to mark their territories and in identifying each other.
Anal sac problems are most common in miniature dogs such as us Dachshunds, bummer! (no pun intended) Yeah right. The sacs normally release a little fluid through small openings whenever your dog has a bowel movement. Sometimes the openings will get clogged or the glands produce more fluid than the sacs can hold. This is very uncomfortable for your pet and leaves them with a feeling of fullness. To express the sacs bring your pet to an area that can be easily cleaned and not hold odor. Perhaps vinyl flooring like in the bathroom. If not put papers around the area that you will be working. Latex gloves work well at keeping the odor off your hands. I like to use tissue around the area while applying pressure to catch anything that sprays out.
Kneeling at your pets side, lift his tail with one hand, using the other hand with paper towels or soft tissues place your hand in the five and seven o'clock position over the anal area. You should be able to feel two bulges if they are very full. With the hand that is holding the tissues, place your thumb and forefinger on either side of the anal opening and press inward. Make sure the anus is covered with the tissues or you may be in for an a very unpleasant surprise! You should actually be able to feel the sacs emptying out and reducing in size. If nothing comes out at first, try again by repositioning your fingers slightly until you have the correct location.
Pushing too hard can be painful and can also damage the sacs, press firm but gently. Continue until no more fluid comes out. I like to apply a little Neosporin or Vaseline to the anal area after expressing to make the area a little more comfortable. http://www.dachshundpages.com/petvet...htm#Anal%20Sac