Japan's All Nippon Airways is asking passengers to empty their bladders before boarding.
The flush-before-you-fly policy started on Oct. 1, the Daily Mail reported.
The thought is that all those empty bladders can add up to big carbon savings.
It might not seem like much, but the human bladder can hold up to 16 ounces before the urge to urinate. That's about 1.1 pounds of fluid. If all 216 passengers on an ANA Boeing 767 had pretty full bladders, that extra urine would weigh about 240 pounds.
The experiment is part of the airline's efforts to "make flying as environmentally friendly as possible," ABC News reported.