Dispensing instruments and methods of introducing fluids and fluid-like materials, as drug material, into the canals of Fallopian tubes are disclosed by Bolduc and Dickhudt in U.S. Pat. Nos. 3,822,702, 3,871,374, 3,875,939, and 3,948,259. These instruments have elongated probes with a forward end carrying expandable balloon assemblies. Dispensing structure located within the housings are used to expand the balloon assemblies and discharge drug material into the uterine cavity. The drug material to be discharged into the uterine cavity is stored in a container accommodated by the dispensing structure. In the use of these dispensing instruments, it is found that the cervices of females have different sizes and strengths. Also, the uterine cavities have different shapes and elongated sections leading to the canals of the Fallopian tubes. Under certain circumstances, it is difficult to insert the balloon assembly through the cervical opening into the uterine cavity. The tight relationship between the balloon assembly and the cervical opening causes any air that is located in the balloon assembly to expand, increasing the difficulty of inserting the balloon assembly through the cervical opening into the uterine cavity.