Maid's Night Out [1938] [DVD]

From imdb ~ Bill Norman, in his rounds as a milkman, finds Sheila Harrison outside a rich-family home doing menial work. She is there because the family is a little bit broke but Bill assumes she is the maid. She also assumes he is just a regular milkman, not knowing he is doing a month's stint on a milk-route on a bet with his father who owns the milk company, who says he can't make good and observe all the company rules. If Bill wins, his father will finance a trip to the South Seas, where he desires to collect fish specimens, which is his hobby. They fall for each other and complications arise; especially after they meet one evening at a charity dance in their true characters, and each gets mad at the other for reasons of deceit on the part of each.