fig1 it can be seen that the punch portion 21a is plugged into the throughbore of sleeve portion 30a a certain extent if retracted toward direction 40 as shown in fig9 the shoulders 24a enter the indentations 39 of adjacent flexible tongues 36 and engage the joint 35 of tongues 36 further retraction is prevented it can be seen further that a passage is defined between the bore wall of sleeve portion 30a and the webs 22a 23a of punch portion 21a the flowable material can flow through the passageways and sleeve portion 30a the interlocking of members 15a 16a shown in fig6 to 10 is achieved by a suitable snap connection in the snap connection the punch portion 21a is formed as a rigid part while member 15a has resilient portions tongues 36 in the embodiment according to fig1 to 4 the punch like member 16 is provided with resilient portions it is understood also that other suitable snap connections can be used furthermore the shape of the punch portions 21 21a can be modified for example an annular cutting edge can be used rather than a cross defined by the cutting edges if for example the bag is not completely emptied the members 15 16 can telescope into one another as shown in fig1 so that the passage for the flowable material is interrupted in order to maintain this closed position an inner projection 12 can be formed in the bore of member 15 which forms a snap connection with the shoulder 24 of member 16 which can be easily released the member 16b shown in fig1 deviates from that shown in fig3 in that the webs 22b 23b are.