I live in Florida on the beach, where flip flops are pretty much a uniform. When mine get dirty and sort of unmanageable, I either throw them in the wash or put them in the dishwasher. The dishwasher is better for the firm soled ones.
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I love shoes. Especially comfortable flip flops. I am always watching other people's feet to see what kind of shoes they have. But I am often appalled when I see someone with cute shoes that are so nasty. Living in Florida I have lots of flip flops and sandals.
Flip flops tend to get dirty, especially my white and pink ones. I have tried many cleaners and the best is the Magic Eraser.