Every time you flush, your poo and pee start an epic journey. From the toilet, to the sewers, to a treatment plant, our waste travels quite a distance only to end up cleaner by the end. We'll hear from a "PooTube" star about her experience with "the flush." We'll also hear about ancient sewers, a "fatberg" under London and a toilet that cleans waste on site. Plus, our Moment of Um answers why you can feel your heart beating in your neck of all places.