This is one of the secret kriyas in Kundalini Yoga that was taught only to a selected few for centuries. It is simple and easy to do. However, it must be done with an empty stomach, not after you've eaten.
Sit in any posture with the spine straight. Make your lips round, in an 'O' shape, and start inhaling the air as if you are drinking it in a series of repeated small sips. Inhale as many sips as you can possibly hold and then stop, close your mouth, hold the breath in, and rotate your belly. Churn your stomach with your breath held in until you can't hold the breath any more. Then very, very slowly and gently release the breath in one stream through the nose. Repeat this cycle again, inhaling in sips, holding the breath, churning the stomach, then exhaling through the nose, for a total of three cycles. This constitutes one complete kriya.
If you want to gain control of your digestive system, practice Vatskar Dhouti Kriya once or twice a day for forty days, but no more than twice a day.
© The Teachings of Yogi Bhajan