Milk run

The phrase milk run originated in World War II, when US Army Air Corps and RAF aircrews used it to describe any mission where minimal resistance from the enemy was expected.
Other sources show the term "milk run" to be in use in the upper Midwest (US) rural areas as early as 1917 and used to describe a train that made frequent stops to pick up farmers' milk cans for shipment to local dairies for processing and bottling. The Macmillan online dictionary describes the American usage as, "AMERICAN an airplane or train trip with stops at many places." In this context, the term was popularly used to describe a slow, tedious trip. The same entry describes a somewhat different British usage: "BRITISH a regular trip during which nothing unusual happens, especially by airplane."
History.
In American urban culture, a milk run came to describe the distribution of milk bottles by the milkman. On his daily route, the milkman simultaneously distributed the full bottles and collected the empty bottles from a previous delivery and would then return with the empty bottles back to the starting point.
In the context of logistics, according to Winfrid Meusel, milk runs were any routes that originated by identifying potential circular tours, whereby the utilization of trucks could be increased and logistics costs could be reduced.
Airline routes.
In the commercial airline industry, "milk run" has been used to describe multi-stop, regularly-scheduled flights performed by a single aircraft. Examples of such routes include: