Today my wife started out the day cleaning the grout in our kitchen tile. We have a pug named Betty and her brother (Rumble) has been over visiting. He is not as good as Betty about waiting and urinating outside. He has been visiting for about two weeks and we now have a build up of urine stains in our white (off white) grout. We had stains in the grout already but not real bad. With Rumble It was looking and smelling bad enough for her to decide she had to clean it up. She first tried a strong alkaline cleaner which helped a little but she was not satisfied at all. Then she tested several products to see what would clean the dog urine out of the grout. She tried bleach and she tried an acid cleaner. These were after the alkaline cleaner. It got a little brighter with each process. Then she got a hydrochloric acid product from a professional stone chemical company. This had a strong smell and she had to wear gloves but she reported that this cleaned up the grout fast and easy and she was thrilled with it. It brightened and whitened the grout right up. It took the urine and everything else that was making the grout dingy out and now it looks like new. It took a little time for the smell of the acid to dissipate but after it did she applied two coats of grout and tile sealer so the future urine would bead up on the grout instead of absorbing in. The hydrochloric acid product did the trick for our dog urine in the grout situation. It cleaned everything else out of the grout at the same time.