An apparatus for washing solid particles collected from a hydrocarbon-containing fluid produced from an oil and/or gas production facility, the apparatus comprising: a vessel having a lower part defining a volume for collecting a bed of solid particles and an upper part defining an exit for liquid from the vessel , a pipe assembly located in the volume, the pipe assembly having a plurality of outlet nozzles located thereon, a pipe network connected to the pipe assembly and arranged to supply pressurised steam or water or a mixture thereof to the pipe assembly to cause the steam or water or a mixture thereof to exit the outlet nozzles into the volume, a fluidising flushing unit located in the volume, the fluidising flushing unit comprising a fluidisation head , an inlet for supplying fluidising liquid to the fluidisation head and an outlet for conveying a fluidised mixture of solid particles and fluidising liquid from the fluidisation head and out of the vessel , an oil content sensing system connected to the outlet of the fluidising flushing unit , the oil content sensing system being adapted to determine whether an oil content of the fluidised mixture or any constituent thereof is below a preset oil content threshold, the oil content sensing system having a first exit communicating with a recirculation pump for recirculating the fluidised mixture back to the vessel and a second exit communicating with an outlet conduit for outputting the fluidised mixture; and a controller for selectively controlling the fluidised mixture into a recirculation flow through the recirculation pump or an output flow through the outlet conduit in response to the oil content determined by the oil content sensing system . a vessel having a lower part defining a volume for collecting a bed of solid particles and an upper part defining an exit for liquid from the vessel , a pipe assembly located in the volume, the pipe assembly having a plurality of outlet nozzles located thereon, a pipe network connected to the pipe assembly and arranged to supply pressurised steam or water or a mixture thereof to the pipe assembly to cause the steam or water or a mixture thereof to exit the outlet nozzles into the volume, a fluidising flushing unit located in the volume, the fluidising flushing unit comprising a fluidisation head , an inlet for supplying fluidising liquid to the fluidisation head and an outlet for conveying a fluidised mixture of solid particles and fluidising liquid from the fluidisation head and out of the vessel , an oil content sensing system connected to the outlet of the fluidising flushing unit , the oil content sensing system being adapted to determine whether an oil content of the fluidised mixture or any constituent thereof is below a preset oil content threshold, the oil content sensing system having a first exit communicating with a recirculation pump for recirculating the fluidised mixture back to the vessel and a second exit communicating with an outlet conduit for outputting the fluidised mixture; and a controller for selectively controlling the fluidised mixture into a recirculation flow through the recirculation pump or an output flow through the outlet conduit in response to the oil content determined by the oil content sensing system . <EOS>