The Hatha-yoga pradipika, a well known treatise on Yoga, defines the sutra neti as follows:-
The Sutra neti is described in the Gheranda Samhita as to
“Draw up the nasal canal a soft string 8 inches long, and draw it out through the mouth.”
This string is specially prepared, as described under. Take a fine cotton thread about 15 meters long and make it nine fold. Twist the nine fold yarn with the help of an assistant and twine it into a rope of three folds taking precautions that all the three folds be smoothly beside one another and do not overlap. Secure the ends of the string by passing each through the twister loop. Trim the loose ends and strongly rub the string with a piece of clean cloth to make it smooth and soft. The string is now ready for use.
Now take a jug full of water. Make the string wet and insert its one end into a nostril. Go on slightly rotating the string for keeping it stiff while you push it up the nose. When the string has gone in about four inches, you will begin to feel its end behind the palate. Catch hold of that end with two fingers of a hand put into the mouth and pull out the string slowly and cautiously. Wash the string thoroughly after it has been drawn out and repeat the same process through the other nostril. This is the ‘samanya’ or simple process of Sutra neti.