To clean grout, you can use a grout cleaner or a bleach solution. Apply the cleaner or solution on grout lines before rinsing it off. When working with bleach, make sure to wear gloves at all times. If grout cleaners or a bleach solution does not work, combine baking soda with water to create a paste. Apply the paste to the stains in your grout lines and allow it to set. You can leave it for a few hours or up to overnight. Then, using a nylon brush or spare toothbrush, scrub the stain and rinse it off.