Use a paste of baking soda and bleach. Make a thick paste from ¾ cup (180 mL) of baking soda with ¼ cup (60 mL) of bleach. Use an old toothbrush or nylon scrubbing brush to work the paste into the grout. Let it sit for 15 minutes, then scrub it. Allow it to sit another 15 minutes, then wipe it off with a damp rag. Frequently rinse out the rag with water as you’re wiping off the paste.
Wear gloves when cleaning with bleach. Open a window or wear a respirator to protect your nose, throat, and lungs. Protect your eyes with safety glasses. Wear old clothes that can get bleached.
Try baking soda and vinegar. Rub baking soda into the grout with your finger. Make it stickier by combining water with the baking soda until you have a thick paste. Next, fill a spray bottle with vinegar and spray vinegar all over the baking soda. Let the mixture bubble for a few minutes, then scrub it with an old toothbrush or nylon scrubbing brush. Wipe up the solution with a damp rag that you rinse frequently.
Scrub it with coarse salt. Wet the grout and surrounding tiles with a damp sponge. Sprinkle it with a coarse salt, then scrub the salt into the grout with a toothbrush or nylon scrubbing brush. Allow the salt to dry overnight, then rinse it off in the morning. Scrub with any coarse salt, even Epsom salts. You can use the same method to clean your grout with Borax. Put a damp scrub brush in a bowl of the Borax and use that to scrub the grout.
Clean and lighten the grout with cream of tartar. Combine two teaspoons (9.85 mL) of cream of tartar with enough lemon juice to create a liquidy paste. Rub the paste into the grout, then scrub it with a toothbrush or nylon scrubbing brush. Rinse the paste off with plenty of water. Use water if you don’t have lemon juice.