When you gotta go, you gotta go–even at 30,000 feet. The alarming noise ensues when you press the “flush” button in an airplane toilet and the bowl’s contents are magically sucked away into oblivion.

However, toilets do get blocked relatively often. “It’s only a tiny pipe, and people put things like nappies down – I’ve seen cutlery go down, and [soft drink cans] – they’re fascinated to see whether ...