Anal breathing is a form of sexual chi kung. Part of it is the contraction exercise (actually exercises) mentioned above. Mantak Chia is one of the taoist masters well known in the U.S. for sexual chi kung. The other parts of sexual chi kung include working with the flow of energy through other foundational exercises that help one to move chi, thus helping to restore energy to the body, including sexual energy.
There is another Taoist practioner who is known for sexual chi kung: Dr. Lin. I'm not familiar with him but I found a site that describes some of his work:
Healing Love: Lin's Links