Windex and a handful of terry towel squares and good ole' elbow grease. It's what I've had to do a few times. The other tip is clean up spills AS they happen and do a spot clean after you cook. And try and mop more than once a week.

Eluned you can by grout paint especially for this. Check out bunnings. Or gel bleach works really well just make sure no one comes in the bathroom.