<p>A suction pump (10) is connected to secretion collection vessel (11) through vacuum hose (12). A catheter (14) is connected with vessel via suction hose (13) arranged near flush hose (16) connected to flush valve (17). A controller (18) is connected to pump for controlling valve according to pressure in vacuum hose measured with sensor (19). The pump is switched ON at intervals so that valve is opened for intake of gaseous flushing medium to reach preset minimum negative pressure. The negative pressure in vacuum hose is measured in pausing immediately after completion of flushing process. An independent claim is included for wound drainage device.</p>
