Drainbow

(slang, of men) To urinate.

A colorful slang euphemism used by men to mean urinating — draining one's bladder. It belongs to the long tradition of inventive, often absurdist slang for going to the toilet, using the 'dragon' as a metaphorical stand-in for the male anatomy. The phrase leans into the macho-absurd register common to locker room and pub banter, treating a mundane bodily function as an occasion for comic bravado. It's rude but not aggressive, and functions primarily as humor.

(slang, rare) A dowdy person.

(chiefly, US, rare) Made up of several races or ethnicities; rainbow.

(often used with “of”) A wide assortment; a varied multitude.