If you’re constantly fighting off rust stains in your bathtub, here’s a cleaning combo that’s sure to do the trick. Mix together equal parts baking soda and cream of tartar. Then add enough lemon juice to make a paste. Rub the paste onto the stain with your fingers or a microfiber cloth, and leave it to sit for about 30 minutes. Then rinse the paste (and the stain) away with warm water.