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).
(From pin idea source: Pour baking soda into a bowl and slowly add hydrogen peroxide until you have the consistency of paste. Spread it over the grout lines and press it in while you’re spreading. Then leave it for awhile. Then using warm water and a cloth simply wipe down the counters being sure to scrub the grout lines as you work.)