Every time you flush, the waste disappears in a swirly whirl, never to be seen again. It’s magic! Actually, it’s science and engineering. And the flush is just the start. Let’s follow that flush! First stop: The sewer pipe. This is where your business mingles with all the other household wastewater. You know, the scummy stuff that gets rinsed off your dishes and clothes and body. In older cities like Chicago, stormwater and runoff joins the party, too. That’s because Chicago has what’s called a combined sewer system.