Planes are full of mystery. We already got to the bottom of why the flight attendant sometimes makes you pull your blind up, and why plane windows are round, but there are other questions that we have.

Flight Attendants Actually Have A Reason For Asking You To Open The Blinds On Plane Windows https://t.co/TZw9HMYtMM pic.twitter.com/XaoLwx05Ay

— Her.ie (@Herdotie) April 11, 2016

So This is Why Aeroplane Windows Are Round https://t.co/S82r50HKyk pic.twitter.com/cNZkXm3c9s — Her.ie (@Herdotie) February 23, 2016

One such question, is how on earth do those plane toilets get emptied? We know, we're disgusting, sorry. Thankfully, there are some curious people out there at The New Zealand Herald who spoke to Air New Zealand at their brilliantly-named 'Pee Lab', to find out how these toilets actually... you know...work. It turns out there's a whole lot of engineering behind the contraption, and each toilet is made up of almost 300 parts, and they each cost $17,000 to manufactured. The engineers, named Duan Russell, Jack Westcott and Peter Lowen are so enthusiastic, and the video is genuinely an interesting watch. The more you know and all that.