Tried it out this morning on my dogs' high traffic/slobber area, worked well! DIY grout cleaner, 5'x6' area. 1/4 cup bleach & 3/4 cup baking soda to create a nice thick paste.Use an old toothbrush and scub. Let it sit for ten minutes, then wipe clean with a rag and hot water (rinse rag constantly).
You probably don't notice your grout getting dark and dirty until it's too late. Just use cotton balls to spread cleaner on the crevices and let sit over night. Wipe off in the morning and you'll wonder why you didn't clean between your tiles sooner. Get the tutorial at On Sutton Place » - GoodHousekeeping.com