the point of view of size corresponds to a developed length ten times shorter than that of the conveying means serving as a buffer used in previous plants the retaining unit 19 may comprise a conveyor 20 extending in an open loop between an inlet 21 and an outlet 22 which can be selectively switched to the conveying unit 3 the open loop formed by the conveyor 20 has a developed length capable of receiving said number of containers which may amount to several hundred in the largest manufacturing units under these conditions in the event of stoppage of the filling unit 2 it is possible to finish emptying the manufacturing unit 1 by interrupting its feed of preforms in such a manner that all containers in the course of manufacture which are present in the manufacturing unit 1 at the moment the filling unit 2 stops can be recovered finished and ready to be used as soon as the plant is put back into operation in this way wasting a not inconsiderable number of containers is avoided and in particular clogging of or even damage to the manufacturing unit is avoided which could occur in the event of stoppage of the latter while still full of containers in the course of manufacture furthermore following too long a stoppage which leads to the cooling of the heating means the manufacturing unit can start to produce containers again only after a preheating period in order to dispense with the disadvantage of such.