There are numerous urban legends about the cleaning virtues of Coca-Cola. Its effectiveness to remove corrosion, though, is proven. I had an experience with surfaces that I couldn’t steer clear using anything else but Coke. Sometimes it works for unclogging as well. But it’s recommended to use at least two liters of Coke and after an hour or two, again, drain with boiling water. A good and affordable method but it might take too long.