Make grout cleaner by mixing 3/4 cup of baking soda with 1/4 cup of household bleach into a paste-like mixture and applying it to the grout surfaces with a toothbrush or scrub brush. Allow the mixture to set on the grout for 10 to 15 minutes, and then rinse away. When working with chemicals, such as bleach, be sure to take proper safety precautions, including covering exposed skin, and keep the area well ventilated to minimize the risks of illness or injury.
Alternatively, use a milder solution of warm water and white vinegar. Mix these ingredients in a spray bottle and apply to the grout. Let stand for five minutes and scrub with an old toothbrush or stiff-bristled brush. You can also use a steam cleaner with this mixture to remove dirt from the grout.
For more cleaning power, make a paste of baking soda and warm water and apply to the grout. Then, spray on the vinegar solution and allow it to set for 10 to 15 minutes. Scrub with a stiff-bristled brush and rinse away. For more difficult stains, use a mixture of baking soda and hydrogen peroxide on the grout. Allow it to set for 10 to 15 minutes and rinse away.
If these homemade household alternatives won't remove grout dirt or stains, it may be necessary to purchase a commercial cleaner. A chlorine bleach cleanser such as Clorox Clean-Up can remove tough stains. However, long-term use of this kind of abrasive cleaner can erode grout, so use it sparingly.