Abstract: The present invention consists in a nozzle for the efficient injection of viscous fluids into holes, cracks or groves through a mechanism preventing the draining outwardly of the volume to fill, which is obtained by incorporating to the injector's tip a screen with a central boring adjusted to the injector tip's surface, preferably of a semi-spherical form and of ferrous material, where said screen shows some freedom of movement levels with respect to the injector, thanks to screen's central boring being surrounded of magnets and having a semi-spherical profile that supplements the injector's tip.