Le Diplomate had an emergency. After a week of frying frites, the kitchen at Washington’s famous standby for French cuisine was full to bursting with used grease.

Two waist-high storage tanks in the back of the restaurant sloshed to the brim with dark, viscous oil. During the weekend rush, the staff stored some of the spent grease in plastic tubs, but they were quickly running out of places to put it.

Restaurants are prohibited from dumping grease down the drain because it would clog city sewers. So on a Tuesday afternoon, James Howell nimbly backed his truck into an alley behind Le Diplomate. He hopped down from the cab and snaked a rubber hose to the kitchen. Then with the flip of a switch and a loud drone, the hose slurped the used cooking oil into the truck’s gleaming steel 2,200-gal

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