Kryas (cleansing practices)

Classic yoga texts, such as the Hatha Yoga Pradipika, describe six kryas. They are:

• Neti (cleansing the nose)
• Trataka (candle gazing, cleanses the eyes)
• Nauli (abdominal churning, strengthens the digestive fire)
• Kapalabati (sharp abdominal breathing, cleanses the lungs)
• Vasti (cleansing of the large intestine)
• Dauti (cleansing of the stomach)

Only the first two are described here.
Nauli and Kabalabati are powerful practices which are best learned directly from a competent teacher.
Here's a link to a good Youtube video explaining Kapalabati Vasti and Dauti are highly specialised practices that are rarely taught.