Basic scouring: sprinkle surface with baking soda, scrub with a rough pad and rinse.
Heavy-duty scouring powder
Combine 1/2 cup baking soda and 1/2 cup washing soda. Use gloves; washing soda is caustic. This formula may scratch fiberglass.
2/3 cup baking soda
1/2 cup liquid soap
enough water to make a paste
Add 2 tablespoons vinegar to paste and stir.
Tip: Use a wet pumice stone to remove tough stains from porcelain or enamel without scratching.