Pour 1/3 cup of ammonia and 1/2 cup of baking soda into the spray bottle.
Pour 7 cups of water into the spray bottle. Mix in 1/4 cup of white vinegar to the spray bottle and quickly tighten the top on the spray bottle to prevent the solution from fizzing out. The vinegar reacts with the baking soda to create a bubbling solution, which is effective for eliminating stains.
Shake the bottle's ingredients and spray the homemade solution directly on the grout. Let it sit for five minutes.
Brush the grout with a toothbrush to lift nail polish from the grout.
Wipe the grout with a wet sponge to clean up any residue.