It sounds obscene, but it’s toilet talk –
an old mechanism for filling water tanks,
somehow invented by a priest in 1790.
A ball-shaped float rises in the tank
signaling the cock-stop. Not obscene. But obscene.

I have always been fascinated with the origins of words, name,s and phrases. That has led me to do occasional posts at another site called Why Name It That? on the etymologies and origin stories of things. (The names of rock bands happen to be the most popular.) I wrote there in more detail about the ballcock (also less obscenely known as a balltap or float valve). It is the mechanism in flush toilets that using a float stops the tank from verflowing by lifting a valve (cock) to shut off the water.