As a general rule, starting an article (or essay or crayon drawing) with a definition from the dictionary is unseemly. It's cheap, it's clunky, it provides no context.
Sometimes at HowStuffWorks.com, we are confronted with such a divisive, hot-button issue that we must abandon style for substance. We must force readers to leap into the topic with a common understanding, and we start with a definition to get everyone on the same page. But we don't get the magnifying glass to inspect the venerable Oxford English Dictionary. We don't pull trusty Merriam-Webster off the shelf. We don't even just copy and paste whatever definition Microsoft Word will provide on a right click. Those dictionaries cannot tell us:
What's a courtesy flush?
Thus referring to Urban Dictionary, a courtesy flush is: "A flush in the middle of the toilet-sitting process in order to reduce the aroma ... usually performed on a 'foreign throne' as a courtesy to the owner of said throne ... in other words, to be polite and not stink up the host's crapper too much" [source: Urban Dictionary]. You can thank message board hero (and, I'm assuming, social historian) "peafarter" for that succinct and well-researched definition, which was given 1,164 enthusiastic "thumbs up" on the site, as of June 2013.
You see, it turns out that some people have different definitions of courtesy flush. (Note that "peafarter" — even "peafarter," people — had 216 "thumbs down.") Some people claim differences when it comes to intention — to avoid aroma or to ensure an unclogged toilet? There are even opposing camps on more fundamental differences. Other Urban Dictionary users (and some real people at a friends' BBQ this weekend) swore a courtesy flush was a secondary flush to make sure any detritus remaining in the bowl was removed.
Which, by virtue of being appointed Author of This Piece, I say is filthy nonsense. We will answer the question "Is a courtesy flush useful or healthy" using the definition put forth by "peafarter."