Abstract: A plug for sealing a sewer or drain conduit and for simultaneously filling the conduit so that the drainage system may be inspected for leaks. A tubular bulb made of an elastomeric material has fluid under pressure supplied to its internal cavity from one end. The bulb expands laterally of its longitudinal axis to thereby seal the conduit in which it is located. Thereafter, a spill over valve coupled to the other end of the bulb releases fluid from the bulb while maintaining the expanded size of the bulb and the sealing engagement between the bulb and the conduit. The bulb may have an external waffle surface to enhance sealing and reduce the likelihood of bulb rupture from sharp pipe edges. The spill over valve includes external channels through which fluid may pass upon sufficient expansion of the overlying bulb. Embodiments are disclosed which include a second bulb for sealing a branch conduit.