Littlejem,
ByGosh,
zauberflöte, and of course anyone else reading this...
Gargling with the salt water often provides temporary relief right away (though not always), but the real relief comes as your body's own immune system more quickly heals the throat because you have simplified its job by using the gargle.
The gargle also helps to remove plaque on your teeth (which causes gum disease) and helps heal mouth sores, all while being isotonic and therefore not irritating to your tissues. A salt water rinse before bed is helpful if you do not have a tooth brush or toothpaste.
I use 1/2 to 3/4 teaspoon salt (I prefer the 3/4 tsp. Saltier water seems more effective at washing away thick mucus.) One cup of pure water, (Warm water may be more soothing, and dissolves the salt a little faster.) Chlorinated water may irritate your throat. Instead use water from a water filter. Chlorine may weaken the immune system.
It has been reported that you can dechlorinate tap water, if you leave chlorinated water out in a wide mouth container, in 24 hours the chlorine will have evaporated away, leaving chlorine-free water. I have never tried this, I have a water filter on my tap, but even a water filter jug is just as good providing the filter is not too old.
Bottled water, use it only if you must, since the plastic bottles (like all plastic) has been reported that they may contain hormone-disrupting and carcinogenic chemicals that migrate into the water. The very thin plastic bottles are the worst, try to avoid these, especially don't reuse those thin bottles.
Mix, Stir. Take as often as you wish, even every half hour. When sick, every three hours probably gives you the maximum benefit, though and when I feel unwell, this is about as frequent as I can tolerate. You can use it daily as a preventative, and especially when you feel a cold coming in, or if you think you might be catching something.
How to gargle: Put a little of the gargle in your mouth, tilt your head back and extend your tongue as you softly blow air up to agitate the gargle so it washes away the mucus. I gargle for about 30 seconds (if I can). Eventually, by doing it multiple times, I stop spitting out mucus (sorry for the graphic description

) try to repeat every few hours.
It is the gentle bubbling agitation of the salt water in your throat that is removing the mucus.