a method of manufacturing a bag for containing liquid , the bag provided with an outlet tube . the method entails seam welding the outlet tube between two superposed bag walls , placing the bag and tube combination between the blocks of a mold , each block having confronting recesses of a particular shape and then injecting molding plastic material to fill these recesses . the injected material forms a collar which completely surrounds the tube and adjacent bag material . the bag film material on either side of the tube is melted to itself and to the tube wall and the collar is thereby securely attached in an encircling configuration thereby to preclude leakage . the tube may be a part of tap or other outlet fitting such as a push pull tap .