Abstract: The present invention relates to a flushing device for internal flushing of tanks, preferably tanks in vessels or ships, whereby a turbine wheel (13) in a turbine device (8) is mounted in a supply conduit (10) so that said wheel (13) is driven by the flow of flush liquid in said supply conduit (10), and whereby the turbine wheel (13) is provided to operate a driving assembly located outside the supply conduit (10) and provided to bring a flush-liquid pipe to rotate and at the same time revolve or turn flush nozzles (7). A magnetic coupling (50) is provided to transfer by means of magnetic power, the rotary motions of the turbine wheel (13) from the interior of the supply conduit (10) to the driving assembly (9) located outside said supply conduit (10). Furthermore, the turbine wheel (13) is displaceably mounted for increasing or decreasing the speed of rotation thereof.