Sealed drainage unit for a hydraulic circuit

Drainage unit adapted to be placed on an enlarged portion of a hydraulic circuit and connecting at least two pipes of this circuit, said drainage unit including a drainage joining piece able to be mounted on each pipe close to the enlarged portion, at least two complementary half-shells, means for closing the half-shells, and imperviousness means inserted between the half-shells and between the joining pieces and the half-shells, wherein the imperviousness means include receptacles containing a humidity-repellent stabilized gel impervious to hydraulic fluid, and projecting portions arranged on said drainage joining pieces and at least one of said half-shells and able to become incrusted inside the stabilized gel by cooperating with said receptacles when said half-shells are closed to prevent any fluid from said hydraulic circuit escaping outside of said drainage unit.