I haven't tried Oxyclean on grout, but it is amazing for getting build-up off glass shower doors. The only trouble is rinsing it off...you're gonna get wet and it takes several attempts to get all the residue off. But nothing cleans quite like it.

Sometimes dry baking soda spritzed with hydrogen peroxide will clean it without residue, but you have to let it sit on the grout in a paste for a while. ITA with sumac, tho. Time to seal.

FWIW, Bill Vincent, one of the tile experts here, always recommends oxyclean for grout.

We used Oxiclean on our white grout (around black wall tile) in our shower, and now have a cloudy white film on the black tile that we cannot remove!!! We have vinegar, industrial cleaner,etc. Nothing works.

I've used a homemade oxyclean paste on grout. It worked but I had the same film problem as you. I've also used comet with bleach to good effect as well. I say go ahead and seal the grout ASAP and perhaps it will buy you some time. I've also tried out the grout tint/sealer and although it is tedious to apply it looks good. If you are going for an off-white/cream there should be one that might work for you. Home improvement stores and tile stores carry various brands. Good luck! I hate dirty grout too. It ALONE is the cause of my current kitchen remodel.

You might try Super Clean on the grout. I bought some to clean grease and oils around the car and tried it on my kitchen floor tile. It worked on both the tile and the grout. It's the sort of stuff you spray on, leave for a few minutes, and wipe away. If you can stand to leave it, it really works a lot better. I expected to have to use my stiff scrub brush on the grout, but an old dish brush worked fine. Super Clean is a step above 409 in cleaning horsepower.

For what it's worth, Oxyclean creates hydrogen peroxide in hot water, so either one of those should work about the same.

I tried the baking soda and hydrogen peroxide in a paste form and left for 45 mins and saw no difference — can I leave it longer?
What is best to paste or mix for the oxiclean?

The Oxyclean is not a miracle on stained white grout in a busy kitchen. But it helped. It is still a bit discolored but does not look so grungy/grimy. It is a pain to get it off after the cleaning process. . I am the one who told the installer to use white grout. He attempted to counsel me otherwise but I "won." I actually wanted a Mexican saltillo tile floor with integrated Talavera tiles. It would have cost twice as much and I demurred. The lesson : Go with your first, best idea. If you have to take option 2 listen to the installer's experienced advice. For all of us with the stained grout-you have sympathetic company.