A corporate stop is shown for sealing an opening in the sidewall of a host pipe. The stop has a threaded stem with an enlarged head portion and a neck portion of reduced size. A flexible sleeve member is received about the neck portion of the stem and has an upper end and a lower end which accommodates the enlarged head portion of the stem. A compression washer has an upper side and a lower side which fits about the sidewall of the conduit. The washer also has an opening which is alignable with an opening provided in the sidewall of the conduit. The lower side of the washer has a recess for receiving the upper end of the sleeve member when the stop is installed on the conduit performing an external seal with respect to the conduit. A clamp nut is engageable with the neck portion of the threaded stem for forcibly moving the lower end of the sleeve member over the head portion of the stem to expand the lower end of the sleeve member and form an internal seal with an opening in the conduit.
