Baking Soda Paste and Vinegar Spray

Make a paste of baking soda and water and apply it directly to the grout lines. Let it sit for a few minutes. Then, spray white vinegar onto the paste. The mixture will fizz, helping to lift dirt and grime. Scrub the grout lines vigorously with a stiff-bristled brush (an old toothbrush or a dedicated grout brush works well). Rinse the area thoroughly with clean water and wipe dry.