This unit is composed of two vats of rectangular form. Each vat includes a mitigated water feeding with nozzle, ﬁ lling tap and overﬂow. A thermostatic mixer is localised on one of the 2 vats and ensures the control of water temperature. An air whirlpool system is integrated into the unit (ref: 1258.03). It is about injection of air under pressure with variable ﬂow through 12 nozzles located at the bottom of the vats (6 nozzles by vat).