Interior tile grout cleaning

Not sure where to post this... But I did an exterior front sidewalk cleaning for one of the national home improvement chains a few weeks ago. They were very happy and paid right on the spot. They asked me if I could clean the floor tiles in their bathrooms. Problem is, for whatever reason, the drains are elevated, so when they tried to pressure wash, they ended up with a mess. Any ideas from you guys? She mentioned maybe an acid cleaning, butttt, idk.
 
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