Green’s Dictionary of Slang

one who washes dishes, usu. in a restaurant, hotel etc.

1961		John o’ London’s 21 Sept. 318/3: But Dunham was more than a washer-upper.
1977		New Society 25 Aug. 381/1: Rubbish-collector, tea boy, washer-upper and so on.
2002		Guardian 27 Jan. 🌐 On her own latest visit to Sandringham she took no fewer than 12 cooks and four washer-uppers.