The small container (0.5 litres) is an item used in the 2016 Easter event. It is used to give Farmer Jimbo the "Eagleade" drink in an attempt to kick him off the tour.
The player must use the 1.5L and 4L containers to fill 3 terminals requiring 0.5L, 1L and 3.5L of Eagleade. That can be done by transferring and emptying the liquids between the two containers given in a precise order detailed in the 2016 Easter event page. Note that the terminals require exact amounts of the drink; ie. the terminal for 1L can't be filled by using Small container (0.5 litres) twice on it. It can be emptied by right clicking on it and selecting "Empty" or using it again on the dispenser.
This container is used to fill the smallest terminal by clicking on it, then clicking on the terminal located next to the liquid dispenser.
The container is not removed from the inventory if players leave the area.