The kit has a hopper (2) provided with a filler pipe (3), an air supply pipe and a ventilation pipe (4). The hopper with the filler pipe and the ventilation pipe is arranged with a ventilation adapter (5) in a plug-in unit (1), which is arranged in a bottom portion of a double wall vessel. The plug-in unit is arranged in a receiving orifice to be arranged with a lower end of the filling pipe. The hopper is equipped with a tooth crown defining an overflow measure. A conically downward tapering sealing sleeve is arranged at the ventilation adapter.
