Plumbing os far more cool than most people appreciate. The key part is hidden, it is called the "trap". a pool of water is held in the pipe in such a way that

Plumbing os far more cool than most people appreciate. The key part is hidden, it is called the "trap". a pool of water is held in the pipe in such a way that gasses from further down cannot travel back up the pipe. https://en.wikipedia.org/wiki/Trap_(plumbing) https://en.wikipedia.org/wiki/Trap_(plumbing) The "flush" we see is a nifty siphon / balance effect. If the toilet tank is dry, you can still flush by pouring a gallon or so of water into the bowl direct, manually taking the place of the tank and clever lever release valve.