I don't really know either, but it seems like I read that when they go to the bathroom, as it passes, it presses against the gland and that takes care of it.
I had to look it up on the internet to see what is was. I remember reading that sometimes dogs will scoot across the floor on their butts and that sometimes people think this is a sign of worms, but that they are trying to express the glands.
thanks so much for all of your help