An elongate flexible conduit including a sealing membrane is positioned through a natural body orifice and along the gastrointestinal (GI) tract of a patient. The sealing membrane is advanced along the GI tract until proximate a target wall segment of an inner wall of the GI tract. The sealing membrane is then permanently or releasably attached to the target wall segment thereby sealing off and isolating the target wall segment from the rest of the GI tract establishing a sterile pathway from the target wall to the natural body orifice. An incision is made through both the sealing membrane and the wall of the GI tract to gain access to the peritoneum to perform surgical techniques without allowing bacteria, stomach acids, and other contaminants in the GI tract to enter the peritoneum. An instrument can then be introduced into the peritoneal cavity through the incision along the sterile pathway.