A device (10,110,210) for the expression of liquids, such as for the maintenance treatment of vascular catheters. A syringe (16; 116a,116b; 216) has a support structure (15,215) and includes at least two separate compartments (11,12; 111,112; 211,212) in which liquids for treating the lumen (L,283) of a catheter (C,280) with which the device is associated. The syringe further includes a closure plug (13,213) to be associated with the lumen being treated, which is coupled, by virtue of a releasable securement arrangement, to support structure (15,215). At least one plunger (16; 116a,116b; 216) is also included for infusing, in preset order, the different treatment liquids into the lumen to be treated, and the syringe further includes a duct (17,217) which is in fluid communication with the two compartments and is arranged through a through hole through the closure plug (13,213) in order to allow access of the treatment liquid to the interior of the lumen (L,283) upon activation of the plunger.