Here's the answer to a hypothetical question you never even realized you were curious about ... What would happen if every American flushed the toilet at the exact same time?
According to the website Life's Little Mysteries, the good news is that it wouldn't explode all of the pipes in the country, ruin the water supply, and flood the streets with human stinky.
In fact, all that would happen is ... it would probably take a little while for your toilet bowl to refill with water.
It's because every city has its own water supply system. Virtually all of them would be able to handle the simultaneous flushing, although they might not have enough water on hand to refill all the toilets.
A few places with older plumbing structures MIGHT see a pipe explosion, but those would be limited. In other words: If 350 million toilets were simultaneously flushed in this country, it wouldn't really be an issue.