April Fools prank by Martin Gardner. <a rel="nofollow" class="external text" href="https://blogs.scientificamerican.com/guest-blog/the-top-10-martin-gardner-scientific-american-articles/">Source</a>
<b>Sketch of the first known depiction of a valve <a href="https://en.wikipedia.org/wiki/en:Flush_toilet" class="extiw" title="w:en:Flush toilet">flush toilet</a></b>
<bdi><a href="https://en.wikipedia.org/wiki/en:Leonardo_da_Vinci" class="extiw" title="w:en:Leonardo da Vinci"><span title="Italian Renaissance polymath (1452−1519)">Leonardo da Vinci</span></a>
</bdi>
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<ul><li>Via Anthony Ravielli from <i><a href="https://en.wikipedia.org/wiki/en:Codex_Madrid_(Leonardo)" class="extiw" title="w:en:Codex Madrid (Leonardo)">Codex Madrid I</a></i>, as lost page discovered in 1975</li>
<li>Via <a href="https://en.wikipedia.org/wiki/en:Martin_Gardner" class="extiw" title="w:en:Martin Gardner">Martin Gardner</a>, in <i><a href="https://en.wikipedia.org/wiki/en:Scientific_American" class="extiw" title="w:en:Scientific American">Scientific American</a></i> (April 1975)</li></ul>