Clorox Precision Pour Bleach Gel is amazing! I have tried EVERYTHING to get my white grout to look clean. In hind sight white grout is the devil but you live you learn. I'm so happy I found something to give this floor it's life back and save me a ton in a new floor!
I literally did the following:
1. Put on gloves and turn bathroom vent on.
2. Put gel on grout and let sit a few minutes.
3. Scrub with toothbrush. Let sit. Scrub one more time with toothbrush.
4. Use bucket of water and old towel to rinse off.
5. Let dry.
*my results were immediate
**face mask would have been smart too