An apparatus for sealing a passageway through an access assembly includes a variable seal member having an orifice for reception of an instrument therethrough. Each of a pair of compression members has a pressure face for contacting the variable seal member, each pressure face opposing the variable seal member from an opposite longitudinal side, and each compression member moveable with respect to the other compression member in a longitudinal direction transverse to the pressure faces. The compression members may be moved in the longitudinal direction to adjust the degree of compressive force exerted on the portal seal member and thus adjust a diameter of the orifice to effectively interface with the instrument to form a fluid tight relation therewith.