Grout brush

We’re big fans of recycling old toothbrushes by using them in some housecleaning chores, but they’re not for every wet cleaning task. They’re better suited to attacking grime in tight corners. Going after dingy bathroom grout with a toothbrush isn’t cleaning, it’s punishment. So go to a home center and spend a few bucks on a grout brush. Grout brushes have larger bristles and longer handles (about a foot to 15 inches) that allow you to speed through the bigger tasks.

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Don Aslett in The Cleaning Encyclopedia: Your A to Z Illustrated Guide to Cleaning Like the Pros.