The device comprises a muff (14) combinable to the rigid tube to bocchettone and at least a metal ring (15) combinable to the flexible tube, a threaded connection (16) aforesaid muff and metal ring in order to connect them mutual and to force them axially against the other, a series of ring-like prominences (17) associates to the metal ring and sporgenti radially towards the axis of the same metal ring in order to engage respective throats (12) separating correspondents undulations (11) of the flexible tube and in order to push the flexible tube waved in engagement of contact forced against saying muff when greenhouse the threaded connection rotating metal ring (15) in connection with muff (14); the ring-like prominences (17) associates to the metal ring introducing a profile conjugated to that one of the separating throats the undulations of the flexible tube. (Rif. Fig. 1).