This is western lore. In the old west there were prostitutes in a lot of small towns and because of lack of infrastructure they would only be able to wash themselves once a year, during winter of all times. Because of the deep snow the wagon was converted with runners to pull it across the snow from town to town. Only one prostitute could wash up at a time though, so they had to take turns. A New Yorker heard of this practice and put it in a song that eventually changed with the times. The line used to be…“Dashing through the snow, in a one-whore soapin’ sleigh.” Merry Christmas and best of the season to all!