A filling nozzle for filling machines, in particular weight-grading machines, for containers such as drums, bottles, cans and/or the like, comprising: a hollow body defining an inner channel for the transit of a fluid, the hollow body being provided with at least one supply duct of the fluid connectable to a respective supply source of the fluid and at least one dispensing opening of the fluid coming from the supply duct; at least one valve member operatively associated with the dispensing opening of the hollow body, the valve member being switchable between a first condition, wherein it sealingly obstructs the dispensing opening of the hollow body to prevent the fluid outflow through the latter and a second condition, wherein it disengages the dispensing opening of the hollow body to allow the fluid outflow from the latter; at least a piston operatively engaged in the inner channel defined by the hollow body, the piston being controllable as for movement and/or switching for isolating the dispensing opening of the hollow body with respect to the supply duct of the fluid and for determining the controlled outflow, from the dispensing opening of the hollow body, of the fluid present between the latter and the piston, wherein the piston comprises: at least a transit channel for the passage of the fluid; at least a valve operatively associated with the transit channel, the valve being switchable between a first condition wherein it closes the transit channel of the piston and a second condition, wherein it opens the transit channel of the piston allowing the transit of the fluid through the latter, characterized in that the piston is movable between a first position, wherein the piston is arranged above the related supply duct of the fluid such that the supply duct of the hollow body is in fluid communication with the dispensing opening of the hollow body through the inner channel of the latter, and a second position, wherein the piston is interposed between the supply duct and the dispensing opening of the hollow body. a hollow body defining an inner channel for the transit of a fluid, the hollow body being provided with at least one supply duct of the fluid connectable to a respective supply source of the fluid and at least one dispensing opening of the fluid coming from the supply duct; at least one valve member operatively associated with the dispensing opening of the hollow body, the valve member being switchable between a first condition, wherein it sealingly obstructs the dispensing opening of the hollow body to prevent the fluid outflow through the latter and a second condition, wherein it disengages the dispensing opening of the hollow body to allow the fluid outflow from the latter; at least a piston operatively engaged in the inner channel defined by the hollow body, the piston being controllable as for movement and/or switching for isolating the dispensing opening of the hollow body with respect to the supply duct of the fluid and for determining the controlled outflow, from the dispensing opening of the hollow body, of the fluid present between the latter and the piston, wherein the piston comprises: at least a transit channel for the passage of the fluid; at least a valve operatively associated with the transit channel, the valve being switchable between a first condition wherein it closes the transit channel of the piston and a second condition, wherein it opens the transit channel of the piston allowing the transit of the fluid through the latter, characterized in that the piston is movable between a first position, wherein the piston is arranged above the related supply duct of the fluid such that the supply duct of the hollow body is in fluid communication with the dispensing opening of the hollow body through the inner channel of the latter, and a second position, wherein the piston is interposed between the supply duct and the dispensing opening of the hollow body. at least a transit channel for the passage of the fluid; at least a valve operatively associated with the transit channel, the valve being switchable between a first condition wherein it closes the transit channel of the piston and a second condition, wherein it opens the transit channel of the piston allowing the transit of the fluid through the latter, characterized in that the piston is movable between a first position, wherein the piston is arranged above the related supply duct of the fluid such that the supply duct of the hollow body is in fluid communication with the dispensing opening of the hollow body through the inner channel of the latter, and a second position, wherein the piston is interposed between the supply duct and the dispensing opening of the hollow body.