The yogic kriyas or cleansing practices are six in number hence called shat-karma (six-actions). These practices are not taught or even referred to in most schools of yog for several reasons. Firstly the practices look difficult, sometimes revolting, un-natural and are definitely not as easy as standing on your head. Many teachers do not know or do these practices themselves. Teaching these practices is also not easy. There is some risk of harm to the student if something goes wrong.
Keeping all this in mind, most yog teachers conveniently overlook these practices. However, it cannot be forgotten that these practices are a part of traditional hatha yog. In fact there they are mentioned as pre-requisites. It is believed that these practices cleanse the body and prepare it for hatha yog. It is as if you are cleaning up your house first before re-decorating it. Surely you will not bother beautifying a dirty house. Cleanliness comes first and hence the importance of kriyas.
THE MOST IMPORTANT THING ABOUT KRIYAS IS THAT YOU MUST LEARN THEM UNDER THE PERSONAL SUPERVISION OF AN EXPERT TEACHER.
You could hurt yourself from an improperly done kriya.
Please do NOT try to learn them from a book or try them out after reading instructions on a web page. For that reason, I am not giving details of the practices here, but rather covering them in brief.
The six kriyas are :
This is the first and most difficult kriya. It involves swallowing and re-gurgitating a fine piece of muslin cloth. I have not tried this practice. My teacher told me that it is prescribed only in case of serious ailments of the stomach like cancer. This is aimed at cleaning the mouth, throat and stomach.
This is the ancient version of enemas or colonic irrigation as it is now euphemistically called. It involves drawing water in to the lower intestine via the anus and then expelling it. This aims to cleanse the lower part of the colon upto the sphincter.
This practice involves cleaning up the nasal passages as well as the throat. It can be done with water (jala-neti), where water is poured into one nostril and it automatically comes out through the other. A variation is Sutra-neti, where a fine thread is taken inside one nostril and then pulled out of the mouth through the throat. Other netis are done with milk (dugdha-neti) or ghee (ghritha-neti). Neti is a pre-requisite for cleaning up the respiratory passages for the proper practice of pranayam.
This kriya is for cleansing and strengthening the eyes. The eyes are focussed usually on a small object or the flame of the lamp in a dark room, without blinking, until they water. Advanced variations involve gazing at a portrait of god or even imagining it in your mind's eye.
The rectus-abdominii (abdominal column) is churned left and right in this kriya. Details are available in classic yoga texts.
Shanka-prakshalan is another advanced kriya that cleans out the entire GI tract. It involves drinking glass after glass of lukewarm salt water and then doing four specific exercises. Then you drink one more glass of the water and then do the exercises again. This is repeated until you feel the urge to go to the bathroom. After you have relieved yourself, you go back to the water drinking and exercises. Again you will feel like going to the bathroom. Notice the consistency of the faeces. This cycle of water drinking and exercises is to be repeated until the water expelled from the anus is as clear as the water you are drinking.
At this stage, your entire gastro-intestinal tract has been fully cleaned. It is as clean as it ever was in your life, apart from when you were a new borne baby.
After this exercise, the body is extremely stressed. You have to rest the whole day. For that day, you should only have a special diet called "khichdi" consisting of boiled rice, lentils (dal) and ghee (clarified butter). This lubricating food replaces the natural lubrication of your insides which has been washed out by the saline solution.
Again, do this kriya only under the supervision of an expert teacher.
This is a cleanser for the respiratory system, especially the lungs. It involves forceful breathing in and out repeatedly. The lungs work like the bellows of a blacksmith. The body is kept in different positions for different effects.
I have personally tried gaj-karani, jala-neti, sutra-neti, trataka, nauli and shankha-prakshalan. I am uncomfortable doing gaja-karani, but others in my family do it easily. I have trouble with sutra-neti too, but my sister does it easily. Jala-neti is easy and can be done by one and all.
My suggestion to you is to have a look at these practices with an open mind. If you feel like it, give it a shot, UNDER THE GUIDANCE OF AN EXPERT TEACHER. I cannot over-emphasise the importance of this. You can do SERIOUS DAMAGE to yourself if the kriyas are performed improperly especially Dhauti.