Some early wringer devices, such as the Rival I have pictured required a wash board and a tub. Some designs came with all three in a wide variety of styles. Believe it or not the first automatic, electric washer was introduced by the Thor company in 1908 but it wasn't until the 1950's that the modern design machine, that both agitated and spun dry a load of clothes in a single tub started to take over the market, eliminating the wringer. Here is a great site documenting the history of washing machines http://www.ideafinder.com/history/inventions/washmachine.htm.
The best and most thorough information I've ever seen about old washing machines has been offered by Lee Maxwell, a retied professor of electrical engineering. Dr. Maxwell operates a museum in Eaton, Colorado and has over 1000 washing machines on display. See http://www.oldewash.com/ for more information.