I'm trying to clean my grout. "Trying" being the operative word. I should just hire someone.
I've given up on the "easy" methods (Hoover FloorMate, steam cleaner) and am now trying a grout brush and sponge. Hopefully when my trial area dries, it'll look clean. [Fingers crossed.]
How'd you make out?
I forgot to mention...if you don't mind me throwing in my 2-cents.
Regarding you grout situation.
If it has grayish / black staining, that's mold and bleach would do it.
If that didn't work; you may have mineral deposits calcium and or rust.
Something like CLR or even white vinegar will clean it.
In either case, it's all about pre-soaking.