A separator device (10) for use adjacent to a sub-sea wellhead (14) includes a vessel (52) in which sand collects in use. The vessel (52) is within a tank (18) in which the fluid phases separate under gravity, so it is immersed in water (22). Ultrasonic transducers (54) on 10 the wall of the vessel (52) are coupled to a signal generator (56) to subject the sand to intense ultrasonic irradiation. This enables the sand (55) to be cleaned, and it can then be ejected (60) onto the seabed.
