When you flush a toilet in the Twin Cities, where does everything go?

Most maps of the Twin Cities feature highways and bridges that connect our region. Few show another grid that is even more crucial to daily life. It transports poop, not people. Host Eric Roper shares some of the most surprising facts about how the system works. Read more: http://strib.mn/39IeRqA. See photos of construction under the Mississippi River: https://pbs.twimg.com/media/DaiSBuZVwAALzCY?format=jpg&name=large