A sleeve assembly is described for coupling a colonoscope insertion tube to an add-on tube. In some embodiments, the sleeve assembly defines an elongated lumen and comprises an inner sleeve sized to receive an insertion tube of a colonoscope, an outer sleeve encircling the inner sleeve, and one or more add-on tubes positioned between the inner sleeve and the outer sleeve. In some embodiments, at least the inner sleeve is collapsible to fit tightly over a colonoscope insertion tube received within the inner sleeve. In some embodiments, the inner sleeve is coupled to the outer sleeve at one or more locations along the length of the inner sleeve so that collapsing of the inner sleeve brings the outer sleeve radially closer to the inner sleeve, approximating the one or more add-on tubes to a colonoscope insertion tube received within the inner sleeve.
