Power grout remover - GIF

Power grout remover.

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Previously:

Applying grout neatly and efficiently - GIF
Automatic grouting tool - GIF
Fast floor tile grouting method - GIF
Grout scraper and spreader - GIF
Masonry grout bag - GIF
Taping grout lines - GIF

That looks like a Rubiscraper Electric Grout Scraper - $183.58 from contractorsdirect dot com (no connection - just first google hit)
Blades for your reciprocating saw run $10-$20 at the big boxes.