The advanced breathing technique in Taoist meditation was explained in a number of classic Neidan texts, including Taoist Yoga, translated by Charles Luk (chapter nine: The immortal breathing or the self-winding wheel of the law). Unlike Prananyama in Indian yoga where withholding of breath being essential to its practice, Taoist method uses a more natural breathing technique with subtle mental control. Needless to say, learning of this advanced breathing technique is not possible without a firm grounding in more preliminary practice. In addition, the classic text was written as training supplement rather than training manual. In this post I will try to lay out the schema of the practice for interested advanced readers.
1. Foundation one: The practitioner needs to have mastered the technique of microcosmic circulation (i.e. breath in and move chi up through the Du Mia, and breath out and move chi down through the Ren Mia), and can do it with ease. （please refer to: The fundamental concept of microcosmic circulation).
2. Foundation two: The practitioner needs to understand abdominal breathing, both straight and reverse type. (please refer to: breathing). And can do both with ease (i.e. without strain and in meditative mode).
3. The name: The name is called "呼吸以踵" (breathing through the ankle) or "呼吸蒂踵" (breathing through the ankle and navel). Both also means continuous breathing. Mentioning the ankle and/or navel meaning chi being activated in the whole body.
4. The concept: The most important concept is continuous breathing whereby the mechanism of breathing in and out of air (through abdominal breathing) is being subtly used to move chi along the microcosmic channels in a continuous manner.
5. The mechanism: (1) Use straight abdominal breathing chi (downward movement of the diaphragm and the pelvic floor muscles) chi is being driven up from the ankle up the perineum and up the Du Mai (督脉) or spinal cord (led up by the third eye). A kind of pulley system: "down" moves "up". (2) Now chi is at the top of the cranium, use reverse abdominal breathing chi (upward movement of the diaphragm and the pelvic floor muscles) chi is being driven down the Ren Mai (任脉） in the front, down to the ankle through the perineum (led down by the navel). In this way, breathing and chi movement is being synchronized into one continuous circulation movement.
Interested readers can refer to chapter nine of Taoist yoga and check up what the classic has to say about this technique.