is in the shape of funnel or connical with a relative large opening 130 at one end and a smaller opening 132 at the other the two portions are disposed so that the smaller opening 132 is adjacent to cavity 128 as shown the diameter of cavity 128 is slightly larger then opening 132 so that shoulder 133 is formed at the interface between the two portions the whole member 118 is formed as a single piece by well known techniques out of a plastic or rubber material the larger opening 130 is chamfered slightly inward as shown by lip 134 plug 122 also comprises two portions 136 and 138 the first portion 136 is in the shape of a rod as shown in fig6 portion 136 is preformed into the shape of the letter j portion 138 has a truncated frustoconnical shape which is joined at its narrower end 140 to first portion 136 preferably the top wider end 142 of portion 138 is terminated by a slanted surface 144 which narrows it slightly the cap is used as follows first tubular member 120 is installed on an empty syringe as shown on fig7 and 8 so that tip 112 is pushed into member 120 until it abuts shoulder 133 in this configuration tubular.