Pull (out) the plug
Q From Brenda Malkiell: I've long wondered whether the expression to pull out the plug refers to the sink or the electrical socket. Any ideas?
A When we use the expression today, it must surely evoke a mental image of the electrical rather than the water sense, which is perhaps why we’re now more likely to say pull the plug (on someone), leaving out the out. When I first read your question, that seemed to be the most likely origin, but then I remembered that to pull the plug was the expression that my mother used for flushing the lavatory (this was in London in the 1940s). To flush an old-style gravity feed water closet before the days of siphons you did indeed pull out, or pull up, a plug that stoppered the pipe from the cistern. The Oxford English Dictionary confirms that the phrase was first used in just that sense. The first citation is from Florence Nightingale’s Notes on Nursing of 1859: “As well might you have a sewer under the room, or think that in a water closet the plug need be pulled up but once a day”, and one from 1919 remarks on “A real Victorian W.C. with a pull up plug”. Another from 1873 refers to a plug in a sink basin. Though there are citations referring to other senses, including the figurative one, not a single one refers to electrical plugs.