(CNN) After spending time indulging in the pleasures of Sin City, tourists heading back home may need to leave a thing or two behind -- like their weed.

The sale of recreational marijuana has been legal in Nevada since last summer , but pot is not legal at Las Vegas' McCarran International Airport.

So to keep travelers from getting in trouble in the airport security line, big green bins -- dubbed amnesty boxes -- were set up a week ago outside McCarran, allowing people to toss their pot before catching their flight. Twenty of the boxes were installed at McCarran and its car rental facility, Henderson Executive Airport and the North Las Vegas Airport.

The bins are about the size of a mailbox, bolted to the ground, monitored and designed to keep what's tossed in them inside the box. In addition to pot, the bins can also be used to drop off prescription drugs.

"We've had a variety of other things disposed of in the bins," Christine Crews, McCarran airport's public information administrator, told CNN. "For example, I was sent a picture of one of the bins containing pills, vape pens, rolled tobacco-looking products, prescription bottles and marijuana-infused drinks."

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