Abstract: A trapping device for trapping foreign liquids having a specific gravity greater than that of a supply liquid comprises a settling chamber defined primarily by a hollow casing, and inlet and outlet chambers in the settling chamber. An inlet and an outlet lead to and from the inlet and outlet chambers, which are separated by an imperforate wall. A heated foraminous wall is arranged so that fluid passing through the chamber from the inlet to the outlet passes through the foraminous wall, which causes separation of the foreign liquid from the supply liquid. The heating of the foraminous wall may be controllable to enable it to be heated sufficiently to clean the foraminous wall. An educer-operated drain is provided for draining settled foreign liquids from the chamber.