Toilets are connected to vent pipes, which connect with outside air. These allow for gravity to work properly in flushing a toilet and they keep swamp gasses out of your house. They can also be an emergency source of air. In 1982, William O. Holmes patented a hose device that would allow you to snake the hose through the toilet trap and breathe the air from the vent pipe.
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Why would you ever want to do that? It’s an emergency device in the event of a fire. Toilet air could be smelly, but the concentrations of noxious gasses are pretty low, and it beats being disabled by smoke inhalation. Still, it seems that the better alternative would be to leave the building entirely. I suppose this invention was targeted at large buildings where people may be trapped from escape, and the fire is less deadly than the smoke where you happen to be. -via Nag on the Lake
Source: neatorama