I ate really badly yesterday. Cantaking diurecic today help flush the water weight gain out?

Not a good idea. Flushing out the water weight , ie urinating, with a diuretic is not a good idea. The water will be quickly replaced in short time, if your body is functioning properly. In addition, essential electrolytes will be compromised which can protentially create problems. "water" in the body is both intracellular and extracellular and equilibrium will be maintained. It's a trick used by charlatans.