“What better than an hour laced with spreadsheets... science focused songs... and a lot of spectacular pyrotechnics” Fringe Review … more

Series 2, Episode 01: FLUSH AND FORGET

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In this episode, Steve discovers the greedy cup siphon hiding inside your loo, Matt delves into Joseph Bazalgette’s calculations for London’s sewer system and Helen teaches everyone how to flush a toilet, through the medium of song.

  • 00:48 – Steve’s bit
  • 11:48 – Helen’s bit
  • 28.03 – Matt’s bit

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Corrections and clarifications:

  • Listener Alex Purcell has pointed out another place where greedy cup siphons can be found… inside condensing boilers.
  • Matthew has suggested Crossness Pumping Station in South East London as a great family day out –  which Helen can confirm as she’s been there several times now. Book your guided tour or open day visit here! Or if you can’t visit, Tim Traveller takes you round it on YouTube, though obviously ignore the bit about how Bazalgette calculated those sewer diameters…
  • If you want even more detail about what happens to London’s effluent after it leaves Bazalgette’s underground sewers, and whether low water use, biogas-generating toilets are the future, this Radio 4 documentary from Helen has plenty.
  • If you enjoy touring sewers around the world, listener Oliver Tasche has suggested Cologne (check out the Chandelier Hall!) and listener Youenn Fenard recommends the “Musée des égouts de Paris
  • Mikael Glamheden emailed from Sweden with a very nicely designed seesaw-style toilet flush. It’s clear, intuitive and accessible. Well done, Swedish design! See below for a picture.
  • Meanwhile, Jaimie Ritchie emailed us an utterly unintuitive toilet flush, as seen in the wild. Any clues about how this works, or confirmation about whether it’s even been installed properly or not, would be very welcome. Pics below!

And here’s a heap of Unnecessary Detail from this episode:

Bazalgette's calculations for the Piccadilly Branch

Bazalgette’s calculations for the Piccadilly Branch


A Swedish toilet flush

A Swedish flush sent in by Mikael, followed by a US flush sent in by Jaimie

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