Fasting or having one meal a day is it good for flushing out kidney stones?

I doubt it. Flushing stones would imply an effort to fluid overload for several days to increase urine volume and the dilution of urine thickness to carry away the stones. Reducing meals or fasting would often reduce fluid intake and thereby increase the thickness of urine, making flushing stones harder.

If you are trying to pass a kidney stone, increase your water intake. Do not fast. Remember, the size, shape and location of the stone also play into whether or not the stone will pass. You should see a urologist who can recommend the proper treatment for the stone.