I'm reading "The Big Necessity" by Rose George at the moment. Her original subtitle for the British edition is "Adventures in the World of Human Waste" but this has become the more urgent "The Unmentionable World of Human Waste and Why It Matters" for the US edition.
The whole book is worth a read but, if you don't fancy it, I can at least recommend you browse chapter two if you come across a copy in a book store. This covers the author's visit to Japan to discover the origins of the washlet. She visits both TOTO and Inax and learns from the latter that they lost the initiative in the market, despite coming up with the basic idea first, because TOTO ran a series of inspired TV ads featuring Jun Togawa while Inax featured a gorilla sitting on a toilet bowl. From the book: "'We don't know why we had the gorilla,' says Inax's senior communications executive. He has been nodding politely for most of the meeting , but the gorilla story unearths a lovely giggle from inside his composure. 'We can't even remember the slogan. But I do remember that he was wearing dungarees'".
TOTO:
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Inax (I can't see the dungarees):
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George writes that it is remarkable how "a nation of pit latrines" where people "defecated by squatting" and "did not use water to cleanse themselves but paper or stone or sticks" came to develop the most advanced toilets in the world in only a few decades. She says it is "the equivalent of persuading a country that drove on the left in horse-drawn carriages to move to the right and drive a Ferrari instead"
George has also dug out a quotation from the author Junichiro Tanizaki which is brand new to me. He wrote about visiting a privy over a river where "the solids discharged from my rectum went tumbling through several tens of feet of void, grazing the wings of butterflies and the heads of passers-by".
The chapter reveals how TOTO gathered data on the average location and angle of people's anuses and also looks at the importance of developing artificial crap to test a toilet's flushing ability. You can also read about the efforts of TOTO to sell the Washlet in America and how the world is divided between people who routinely wash with water and those who use paper. In 1964, a British physician surveyed the underpants of 940 men and found "faecal contamination in nearly all of them that ranged from 'wasp-coloured' stains to 'frank massive faeces'. This led the doctor to complain that "a high proportion of the population are prepared to cry aloud about footling matters of uncleanliness such as a tomato sauce stain on a tablecloth, whilst they luxuriate on a plush seat in their faecally stained pants".