Abstract: An improved device of a combination of elements is adapted to be used with an elongated flexible instrument, such as an endoscope, and capable of at least partially extending with the instrument into the lumen of a tubular body part, such as the large intestines. A sheath is adapted to be mounted on the instrument. The instrument and sheath are provided with selectively inflatable cuffs movable with respect to one another by axially sliding the sheath on the instrument. The movable relationship of the sheath and instrument and the selective control of air to the cuffs allows the user to more easily navigate the front of the instrument through the lumen of the body part with less discomfort to the patient.