Abstract: In apparatus for applying, by flood coating, a layer of a corrosion-inhibiting material to internal surface regions of cavities in a metal structure via passages communicating with the cavities, which apparatus includes at least one conduit having an outlet end arranged to communicate with one such passage for feeding corrosion-inhibiting material through that passage and into a cavity communicating therewith, the conduit is constituted in the region of its outlet end, by a main conduit portion extending upwardly at an angle to the vertical and arranged to convey material from a supply tank, and a pipe section which is open at both ends and is oriented with its longitudinal axis substantially vertical, the main conduit portion being connected to the pipe section at a point intermediate its ends for conveying material in an upward direction into the pipe section, the upper end of the pipe section constituting the outlet end of the conduit, and the lower end of the pipe section constituting a drain opening via