A base for a pressurized gas tank, such as hydrogen, is substantially circular about an axis, and comprises a substantially cylindrical pipe of axis, which passes through the base in order to connect an outside of the tank to an inside of the tank. A substantially tubular notch of axis is arranged on an inner side of the tank and is suitable for receiving a sealing envelope. A substantially tubular sleeve of axis is arranged on the inner side of the tank and has an inner diameter substantially equal to a diameter of the pipe and an outer diameter substantially equal to an inner diameter of the notch, and also has an axial extension at least equal to that of the notch. An O-ring and a groove of axis, capable of receiving the O-ring, are arranged in a side wall of the notch. The base also comprises a body and a substantially tubular ring of axis, interfaced by a surface of revolution about the axis passing through the groove.