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Modern Boeing and Airbus aircraft employ a suction system for the lavatory on board. How is this suction system powered? By utilizing an on board suction pump or natural pressure and velocity difference from outside the aircraft during flight?

One way to find out would be to try a flush while plane is on a taxiway, but access to the lavatory during that period is not allowed.

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  • $\begingroup$ Maybe that's why it's not allowed? :) $\endgroup$ – egid Mar 6 '15 at 17:27
  • $\begingroup$ I'll add that I often see people using the lavatory while the plane is still at the gate -- flight attendants could prevent it if they wanted to by locking the lavatory doors, but in my experience, it's allowed (though they do get cranky if passengers don't finish up by the time they are ready to push off from the gate since all passengers have to be seated). If the toilets were inoperable on the ground, the lavatories would quickly become a health hazard when passengers are stuck in the plane during multi-hour ground delays. $\endgroup$ – Johnny Mar 6 '15 at 18:59