In the present invention, use is made of a flushing device which permits flushing with two different amounts of flushing fluid. The bottom valve member (21) of the device comprises two float rods (30, 31) which are each connected to a float (32, 33). The float rod (30) for the small flushing amount is fixedly connected to the bottom valve member, whereas the float rod (31) for the large flushing amount is connected to the bottom valve member via a lost-motion coupling (37) to make it possible for the bottom valve member to move upwards and downwards relative to this float road. In the resting position, the float rod (31) for flushing with the large amount of flushing fluid is locked by means of a lock (59), such that the float (33) connected to this float rod does not affect the lowering of the bottom valve member (21) towards its valve seat (20) during flushing. The flushing with the small amount of flushing fluid will thus be determined completely by the movements of the other float rod (30) and its associated float (32). When releasing the mechanism for flushing with the small amount of flushing fluid, a release member (55) is actuated, which first releases the above-mentioned lock (59) and then raises the bottom valve member (21) from its seat (20) by means of the float rod (31) intended for the large flushing amount.