Richard Van Remmen keeps his white lawn chairs outdoors all winter so they collect as much mold, algae, pollen, pine sap and dirt as possible. Come spring, he clamps a small camera to the wand of his pressure washer and records himself spraying the grime away.

“When you’re watching, it’s like you’re doing the pressure washing, but you’re not,” says Mr. Van Remmen, a tax-preparation professional in Rock Hill, S.C., who posts his cleaning footage online. One of his videos has been watched more than a million times.

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