BY.

IT IS THE SOUND OF CHICAGO!

THAT'S ALL FROM EDGEWATER.

PARIS, BACK TO YOU.

>>> OUR DIGITAL SERIES WTTW EXPLAINS HAS TAKEN ON EVERYTHING FROM CARS ON SUNDAYS TO THE DETAILS OF LAKE EFFECT SNOW.

WE HAVE NOT COVERED TOILETS.

SO GATHER ALL THE NEIGHBORS AND KIDS AS PATTY WHITLEY BRAVES THE DEPTHS OF THE SEWER SYSTEM.

>> Reporter: EVERY TIME YOU FLUSH, THE WASTE DISAPPEARS IN A SWIRLY WORLD, NEVER TO BE SEEN AGAIN!

IT'S MAGIC!

ACTUALLY, IT'S SCIENCE AND ENGINEERING.

LET'S FOLLOW THE FLUSH.

FIRST STOP, THE SEWER PIPES.

HERE IS WHERE IT IS WITH ALL THE OTHER HOUSEHOLD WASTE WATER, YOU KNOW, FROM WHEN YOU RINSED OFF YOUR DISHES AND CLOTHES.

THEN, CHICAGO STORMWATER AND RUNOFF JOINS THE PARTY, TOO.

ALL OF THIS WASTE GETS SWEPT INTO HIS OWN OWNED BY THE METROPOLITAN WATER RECLAMATION DISTRICT OF GREATER CHICAGO.

MORE THAN 1 BILLION GALLONS OF WASTEWATER ARE PRODUCED EVERY DAY WITHIN THE CHICAGO METRO AREA.

BEST CASE SCENARIO, THIS CA-CA COCKTAIL IS HEADED TOWARDS A RECLAMATION PLAN.

WORST CASE SCENARIO, IT COULD FLOW INTO WATERWAYS LIKE THE CHICAGO RIVER.

THAT IS WHAT HAS HAPPENED IN THE PAST, WHEN ALL THE TOILET TREASURES WENT STRAIGHT INTO THE RIVER AND INTO LAKE MICHIGAN.

BUT LET'S STAY FOCUSED ON THE POSITIVE.

TODAY WHEN WASTEWATER REACHES WATER RECLAMATION PLANTS, LARGE SCREENS FILTER THINGS OUT.

SOLIDS SETTLE TO THE BOTTOM AND ARE FUNNELED AWAY.

IF ANYTHING SOMEHOW STAYS AFLOAT, THERE ARE, AND THERE IS NO BETTER WAY TO SAY THIS, POOP-EATING MICROBES.

THE MICROBES THEN DROPPED TO THE BOTTOM AND THE CLEAN WATER ON TOP FLOWS INTO THE WATERWAY, BUT NOT LAKE MICHIGAN.

REPEAT, NOT LAKE MICHIGAN.

THE WHOLE PROCESS TAKES ABOUT 12 HOURS.