Note that professional-grade, commercially available eye washes are always preferable to homemade remedies. No matter how meticulous you are, there's always the risk of accidentally irritating the eyes or giving yourself a potentially severe infection. There are reported cases of people trying to make saline solution at home and getting acanthamoeba infections. This is a risky procedure. However, if you understand the risks and still want to make your own eye wash solution, there are measures you can take to ensure that your solution is as clean and safe as possible. Begin by boiling a pot of water to kill bacteria and other organisms in it that can contaminate your eyes. Bring the water to a full rolling boil for at least one minute and then cool before use.  If possible, it's better to use sterile, purified water rather than ordinary tap water. Tap water can contain more bacteria and additives than sterile water. If you don't want to make an eye wash solution, you can always substitute tap water. Just understand that it may be more irritating and it carries a higher risk of containing bacteria, etc. For homemade eye washes, add one teaspoon of ordinary table salt for each cup of water while the water is boiling. The closer your solution is to the natural salinity (salt concentration) of your tears, the lesser the shock to your eyes. Though the salinity of tears varies based on whether the tears are produced as the result of emotions (pain, sadness, etc.) or merely as a lubricant for the eye during normal use, tears are usually less than 1% salt by weight. Ensure the salt that you add dissolves in the water. Since the water is boiling and you've added a relatively small amount of salt, it shouldn't take much stirring to dissolve it completely. Stir until you no longer see solid salt grains at the bottom of the pot. Never use an eyewash that's still hot. You can seriously injure or even blind yourself by burning your eyes with hot water. Remove your solution from heat and allow it to cool to room temperature....

How would you rephrase that briefly using Vietnamese?
Nấu sôi nước. Thêm muối vào nước. Khuấy tan muối. Để dung dịch nguội.