Abstract: The present invention relates to a device for periodically rinsing a water cock countersunk in the ground. A drainpipe is connected between the water cock and a closing member of an extension piece. The drainpipe includes a valve body which is opened by the water pressure prevailing in the extension pipe when the water cock is initially opened. After a predetermined period of time the valve body is closed. Thus, the present invention ensures that after the water cock is opened dirt is flushed away through the drainpipe which is subsequently automatically closed after a predetermined time. After the drainpipe is closed, a valve member connected to the extension pipe can be opened and only pure water will be supplied.