This practice is also known as "varisar dhouti" - Part of Dhauti Kriya
WARNING! No one should try this in absence of Yoga Guru and without the advice of a medical practitioner. Make sure there are no stones in the kidneys or bile. Be careful if you have high blood pressure. All the procedures you do at your own risk. Listen to your body and do not overstrain yourself. This is not the ultimate guide to action. Check the information and use your brain!
In short
It's recommended to do the procedure after finishing Ekadashi day. Ideally in the early morning after the 36 hours of water fasting, fresh juice day or light vegetarian diet without beans, mushrooms and grains.
Make sure that adequate toilet facilities are nearby ;)
Start the process early in the morning at 6 to 7am.
Take 1 liter of pure warm water (distilled if have), mix with 2 tablespoon of salt (Himalayan salt if have) and juice of one lemon. Drink all (even if it disgusting) in a sitting position. You may lie down for 30-60 min on a right sight, put under the area of your liver something warm, cover yourself with a blanket and sweat a bit.
After that drink water (distilled if have) unstoppable. 4-5 liters in total. One or two glasses each 5-10 min.
Do special asanas sequence after each 1-2 glass (video below)
Repeat #6 until by the following visiting of the toilet the clean water come out.
After procedure take a rest for a while (about 1 hour) and you may start eating. Start with one banana to launch your digestive system. Do not pounce on the food. Gradually with a breaks increase the load on the stomach (raw fruits -> raw veggies -> cooked food ...)
Benefits
Shankhaprakshalana is not just a practice concerning the stomach and intestines but is a thorough cleansing technique. It creates a repair action which affects the lungs, nervous system, skin, sinus area, the whole body, continuing while the person follows the regime of special food and asanas. In this way we see the reduction of so many disease conditions, diabetes being the most notable, and a positive step in the direction of good health.
The benefit for the serious yogic practitioner is a lighter, more flexible, physical body. The various metabolic acids and chemical wastes causing stiffness, lethargy and heaviness such as lactic acid and uric acid are washed away. A clearer and more alert mind is experienced as with fasting but without the irritating feeling of an empty stomach.
As intake of toxic substances must be curtailed, it is at this time that many people leave cigarettes, alcohol and other habits permanently. This is a time of revision where life changes direction, new food, new habits and the foundation for a positive fresh view of life are set.