this method consists essentially in manufacturing dripper units and attaching them longitudinally to a thread by positioning them at intervals along the latter . for this purpose , the thread is introduced into at least one notch of the dripper unit so as to clamp it . the width of the notch is less than the diameter of the thread . the thread fitted with dripper units is introduced into the tube while the latter is being formed in an extruder so as to draw the dripper units therein one after the other . the dripper units are then heat welded to the inner wall of the tube during its formation . the insertion of the thread into the notch is achieved via a wheel onto whose the edge it is guided . in this manner , the whole method can be implemented continuously without any intermittent operations .