Sea-salt or saltwater flushes are promoted for internal cleansing and for treatment of colds, high blood pressure, and other health problems. The drill is to add a teaspoon (or two, depending on the plan you're following) of sea salt or non-iodized salt to one or two quarts of water, drink it, and wait for it to run through you, taking "toxins" with it. Depending on the plan, you do this daily for a week or longer.
I once tried a flush of half sea water and half fresh water, which did cause a pretty rapid flush (that is, a watery bowel movement within 30 minutes). I am concerned about the sodium load of this and the sea-salt flushes I've seen described online. A single teaspoon of salt gives you 2,400 mg of sodium, more than enough for a day's intake (I recommend limiting your daily intake to 1,500 mg of sodium).
In evaluating claims for flushes and other cleansing regimes, be aware that the body does a pretty good job of cleansing and purifying itself. If you focus on good nutrition, regular exercise, and other healthy habits, you won't feel the need to do this sort of thing.
If you really want to do an intestinal cleanse, I suggest a daylong or weekend "juice fast" plus some powdered psyllium seed husks to give your intestines bulk. Stir a tablespoon of the powder into a big glass of water, drink it and then drink another glass of plain water. Do this once a day, preferably in the morning. While you fast, take 100 mg of vitamin C twice a day, but skip your other supplements.
Drink at least four 8- to 12-ounce glasses of juice daily plus at least four 8-ounce glasses of water and, if you like, some unsweetened herbal tea. If possible, prepare the juice yourself from organically grown fruits and vegetables. One combination I like is apple, carrot, and lemon juice, diluted with plain or sparkling water.
If you can't make your own juices, buy natural ones without added sugar and dilute them to taste with water. While fasting, a daily sauna or steam bath can help the body eliminate unwanted materials through sweating (be sure to drink extra water during and after). Be sure to eat lightly and carefully when you end your fast and transition back to your normal diet. Going straight to pizza or enchiladas will almost certainly cause discomfort.
By the way, I don't recommend colonic irrigation for "purification." The entire lining of the colon sloughs off and is regenerated every day. If you are eating well, drinking enough water, and getting enough physical activity, your regular eliminations will be sufficient to keep the colon clean and in good working order.
Andrew Weil, M.D.