Drainpipe test plug with pressure assisted plug seal

A drainpipe test plug for plugging a drainpipe via an opening formed therein includes a plug seal that includes a planar front surface which faces upward in the drainpipe whenever the drainpipe test plug is in a plugging position and a peripheral annular rim. The plug seal can include a plurality of holes or a continuous channel formed into the surface of the planar front surface, or a plurality of holes or a continuous channel formed into the surface of the peripheral annular rim, or both. The plug seal holes or channels impart a degree of flexibility to a peripheral area of the plug seal to facilitate the insertion and removal of the drainpipe test plug from the drainpipe. In addition, the holes or channel in the planar front surface provide additional sealing force against the interior of the drainpipe whenever the drainpipe test plug is in the plugging position.