Basti is an important part of Shatkarma (sometimes known as Shatkriya), the yogic system of body cleansing techniques. It is intended mainly to the cleaning of the lower abdomen, especially the colon. Both the Hatha Yoga Pradipika and other sources usually attribute to it many beneficial effects. There are basically two techniques to perform Basti:
Sthala basti (aka Sushka basti or Vata basti), cleans the colon by sucking air into the body without the help of any external aid in the form of a catheter or tube.
Jala basti (aka ‘Vati basti’) cleans the colon by sucking water into the anus. It is allowed the use of a catheter tube.
Definition courtesy Wikipedia.