Breathing filter for a tank

A one-piece paper filter element (50), of inverted cup form with a plane top face (51) and fluted side wall (32), for use in a two part plastics housing (13,14) e.g. polyamide or glass re-inforced or polyamide. The housing is a tank breather cap, which separates for introduction of the element and then clamps the filter during re-assembly. Independent claims are included for the process of manufacturing a frustro-conical filter element with a plane minor end face (51) and corrugated skirt (32), and for tank breather filter elements which can be push -fitted into a cap and retained between clamping surfaces (36,39) constructed on the housing components (13,14).