Vinegar & water, or grout haze remover, or as a last resort only: miratic acid (read all instructions on label it's very powerful acid. Good luck!
Lots of water
Try a wet sponge, first. If that doesn't get it all, then use one of those green scotch pads for any residue, after the grout has set.
After you grout, and went back with a wet sponge , if you still have a film, use a scotch Brite pad and go over it again. Thats if you're grout has set up already.
I personally do not know. Call Lowes, the have people who know.
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