Mix 1/2 teaspoon of salt, 1/2 teaspoon of sugar and 1/2 teaspoon of sodium bicarbonate in 2 pints of boiled water that has been left to cool.
Pour the mixture into a sterilised bottle and keep in the refrigerator. The mixture should keep quite well for up to 2 weeks, but ideally should be changed every few days for hygiene reasons.
Source: Dr. A. Simon Carney FRCS, FRACS, Consultant Senior Lecturer and Specialist in ENT Surgery.