of the pipe 10 by cutting a cylindrical section out of the pipe to form the opening 28 if the line is filled with fluid at the point of formation of the opening 28 it may also be necessary to provide a so called sandwich type tapping valve mounted on the saddle member 22 such a valve is referenced in connection with the procedure described herein in conjunction with fig7 of the drawings after the opening 28 is formed the aforementioned tapping machine is removed and the bag insertion apparatus 18 installed on the saddle member 22 the bag tube 24 is then extended into the interior 12 of the pipe 10 and the bag 14 is ejected from the interior of the tube into generally the position shown in fig1 by suitable means such as the introduction of pressure fluid into the tube interior 26 by way of a suitable conduit 27 for example a suitable freezable liquid such as water is then conducted through the conduit sections 48 and 62 to fill the bag 14 so that it assumes generally the shape indicated in fig1 although when the bag 14 is in the collapsed condition within the interior of the tube 24 there is very little air within the bag the passage 50 66 defined by the conduit sections.