I was in a bar in London recently (in a decent restaurant on Charlotte St) and ordered a Hendricks martini. The barman made it with great care - lots of ice, no rushing, generous pour - but took one step that quite startled me: he added the vermouth to the mixing glass full of ice, let it sit a minute, then POURED IT DOWN THE DRAIN before adding the gin and straining the result into a serving glass.
I blinked a bit didn't question him, and it was tasty and cold on a hot day, so I forgot about it until I was just reading a post a couple of minutes ago in which someone mentioned this technique and called it an "in and out," at least when done with vodka instead of gin.
I can understand someone wanting just a hint of vermouth in a martini (I prefer more, but de gustibus), but this strikes me as a rather wasteful way to get that result.
Is this a known variation on this side of the Atlantic?