The story
They are said to hook up with a washing machine.
Etymology from Wiktionary, CC BY-SA 4.0.
hook-ups
Today it means: A pair of miniature valves right next to each other on a wall, connecting through the wall to the household plumbing, used to provide water to a washing machine. (They are usually red and blue, with the red one delivering hot water and the blue one delivering cold water.) Full definition →