Method for operating a dirt collecting device for a sweeping vehicle or for a vacuum cleaner nozzle of a floor or upright vacuum cleaner, which each comprise a suction fan with controllable speed and/or power, wherein in a first method step, the suction power of the suction fan is set at such a low level that the suction pressure in the dirt collecting device or the vacuum cleaner nozzle is merely sufficient to convey and deposit the absorbed coarse dirt into the intermediate container, and to convey the absorbed fine dirt into a downstream collection container, (normal operation); and that in a second method step, the filling level in the intermediate container is detected with respect to the coarse dirt deposited therein; and that in a third method step, if the filling level in the intermediate container is exceeded, the suction power of the suction fan is increased such that the coarse dirt, which is temporarily deposited in the intermediate container, becomes dispersible and is conveyed into the downstream collection container (emptying mode).