u00b0 according to this illustrated embodiment a predetermined number of said hollow parts are placed beforehand on a support which includes at least one retaining member capable of immobilizing each of them fig1 illustrates a first embodiment given by way of example of a tank 1 intended for implementing the treatment process according to the invention according to this embodiment the tank for treating the hollow parts which bears the general reference 1 comprises mounted so as to rotate inside the tank a drum 10 to which each hollow part can be fastened according to the embodiment illustrated the drum 10 comprises on its external periphery 100 at least one housing track 11 to which each hollow part can be fastened more precisely the drum 10 includes fastening means 12 integral with the housing track 11 which are capable of fastening each support 2 for the hollow parts by sliding with interlocking of the support 2 into the track 11 in the embodiment illustrated the support 2 is as described in patent application ep a 1 433 537 for the sake of clarity the hollow parts treated according to the invention have not been shown here only their supports 2 being shown see fig1 d it goes without saying that all the movements undergone by each support are also undergone by the parts fastened to each support the tank 1 according to the invention includes its own motor means 13 here an electric drive motor which rotates the drum 10 the tank 1 also includes in the embodiment illustrated its own transmission means 14 15 which transmit the rotational movement of the motor 13 into a rotational movement of the drum 10 here in the illustrated embodiment of the invention the drum 10 is cogged 15.