Crappe for chaff and dregs is Middle English, attested from the fifteenth century, from Dutch krappe. Thomas Crapper, 1836 to 1910, was a genuine sanitary engineer with royal warrants and plumbing patents, but the vulgar sense of crap is recorded before his career, and he invented neither the word nor, despite the legend, the flush toilet.
The Crapper story is too good not to tell, and it grew: he invented the flush toilet, American doughboys saw his name on cisterns and brought the word home. Each layer is false or distorted, flush toilets predate him by centuries, the word predates him by more, yet his name genuinely did decorate plumbing fixtures.
Eponymy researchers use Crapper as the standard example of a name that reinforces a word it did not create, the nominative-determinism illusion in reverse: not the name shaping the fate, but the fate retroactively assigning the name.
A man's surname accidentally matched a slang word, and the world decided he must be its father. What does that say about how we assign credit?