Pull the Plug

The other day I started thinking about the phrase "pull the plug". Most people think the phrase has to do with pulling out the electric cord and turning off the power on something and specifically many think of "pulling the plug" on someone plugged into life-support equipment at a hospital.

I, however, think the phrase originated with a bathtub or sink plug that you'd pull when you were done with your bath or whatever.

Couldn't find a definitive answer to this question but since there seems to be some use of the phrase in the 18th century - I'm going to go ahead and say that I was right. And now that I've written all this down - I can finally stop thinking about this stupid phrase.