you are not a true Rockabilly fan if you don't know that the washboard was frequently used as an instrument in the 50s. You can buy those nowadays as well, but they can barely be used for the original purpose. But who is washing manually recently?
The song where the washboard will be used is the Washmachine Boogie. It was performed by the Tom White and the Mad Circus in the Amigo bar, on 03/01/2020.