The bad odor and stubborn discoloration that dog urine leaves on tile grout generally does not clean off completely with standard cleaners from the department store; the lingering residue is what makes your dog do his business there again. Use an enzymatic cleaner to clean the surface. Then, if the stain is really stubborn and still there, try an acidic professional grade cleaner to save your tile and grout.
Try an Enzymatic Cleaner First
An enzymatic cleaner is a good starting point for urine stain removal because it's considered a safe, natural and powerful, cleaner. This cleaner works because the enzymes basically eat the stain. Just spray on a generous coat of the cleaner, completely saturating the urine stain in the grout, then allow it to dry naturally. Check the cleaner's label for specific directions as products vary, but you normally do not have to scrub the stain or rinse off the cleaner.
Really Stubborn Urine Stains
Visit a professional stone chemical company or the industrial chemical section of a hardware store. Pick up a container of hydrochloric acid, which is also called muriatic acid. Put on some personal protective gear, including gloves, eye protection and a face mask, as this chemical is considered dangerous when inhaled or contacting skin. Check the directions for using the acid and follow them carefully. Apply the chemical and rinse off residue according to the package's directions. Air out the room. Reseal the grout to prevent future urine saturation.