Well it looks like Rachel tipped you off already about the section on this site about them. They are indeed called scent glands and unfortunately they do no empty themselves. They are not located too closely to the anus of the rabbit, rather they are on either side of where the genetalia is located. They are pockets and so may take some gentle stretching and prodding to find. I recommend either wetting the Q-tip with warm water, pure aloe vera gel or Vaseline. If there are really big, hard chunks, let them soak first in some Vaseline for a few minutes before removing. You might want to keep a plastic bag handy, it is quite a smelly operation. The stuff that you may see is hard and brown/black or yellow in color and like soft cheese in texture. Let us know if you have any trouble! I’ll take a peek at what BB has, its been a while since I already know how to do it and if the illustrations aren’t too good, I’ll try to find some others for you.
These are actual photos and may not be for the faint of heart or those of you who do not like to see anatomy:
http://members.aol.com/roniebunny/ng.html