An overtube for use with an endoscope having an exterior surface and for insertion through a patient's natural body orifice, said overtube comprising: a) a tubular member having a proximal portion and a distal portion, and a length therebetween sufficient to extend from a patient's mouth to a patient's stomach, said tubular member defining a central passage for receiving the endoscope therethrough; and b) a hub assembly coupled to said proximal portion, said hub assembly including a longitudinally symmetrical rigid body member having a first end, a second end, an inner surface defining a smooth central passage, an exterior surface, and a fluid connector, a flexible sleeve extending within said central passage of said body member, said sleeve having an outer surface, an inner surface, and first and second ends, said first and second ends coupled relative to said body member, and said outer surface of said sleeve and said inner surface of said body member are in communication with said fluid connector, an inner collar partly extending into said proximal portion of said tubular member, an outer collar extending over said proximal portion of said tubular member and said inner collar to engage said proximal portion of said tubular body to dispose the proximal portion between said inner and outer collars (32, 34), said inner collar is coupled in a snap-fit engagement to said first end of said body member, and said outer collar is coupled in a snap-fit engagement to said inner collar to secure said proximal portion of said tubular member therebetween, and a proximal hub collar defining a proximal mouth through said hub assembly, said hub collar locked in a snap-fit engagement to said second end of said body member, wherein when a fluid is provided under pressure through said fluid connector, said sleeve distends radially inward to define an opening smaller than said central passage. a) a tubular member having a proximal portion and a distal portion, and a length therebetween sufficient to extend from a patient's mouth to a patient's stomach, said tubular member defining a central passage for receiving the endoscope therethrough; and b) a hub assembly coupled to said proximal portion, said hub assembly including a longitudinally symmetrical rigid body member having a first end, a second end, an inner surface defining a smooth central passage, an exterior surface, and a fluid connector, a flexible sleeve extending within said central passage of said body member, said sleeve having an outer surface, an inner surface, and first and second ends, said first and second ends coupled relative to said body member, and said outer surface of said sleeve and said inner surface of said body member are in communication with said fluid connector, an inner collar partly extending into said proximal portion of said tubular member, an outer collar extending over said proximal portion of said tubular member and said inner collar to engage said proximal portion of said tubular body to dispose the proximal portion between said inner and outer collars (32, 34), said inner collar is coupled in a snap-fit engagement to said first end of said body member, and said outer collar is coupled in a snap-fit engagement to said inner collar to secure said proximal portion of said tubular member therebetween, and a proximal hub collar defining a proximal mouth through said hub assembly, said hub collar locked in a snap-fit engagement to said second end of said body member, wherein when a fluid is provided under pressure through said fluid connector, said sleeve distends radially inward to define an opening smaller than said central passage. a longitudinally symmetrical rigid body member having a first end, a second end, an inner surface defining a smooth central passage, an exterior surface, and a fluid connector, a flexible sleeve extending within said central passage of said body member, said sleeve having an outer surface, an inner surface, and first and second ends, said first and second ends coupled relative to said body member, and said outer surface of said sleeve and said inner surface of said body member are in communication with said fluid connector, an inner collar partly extending into said proximal portion of said tubular member, an outer collar extending over said proximal portion of said tubular member and said inner collar to engage said proximal portion of said tubular body to dispose the proximal portion between said inner and outer collars (32, 34), said inner collar is coupled in a snap-fit engagement to said first end of said body member, and said outer collar is coupled in a snap-fit engagement to said inner collar to secure said proximal portion of said tubular member therebetween, and a proximal hub collar defining a proximal mouth through said hub assembly, said hub collar locked in a snap-fit engagement to said second end of said body member, wherein when a fluid is provided under pressure through said fluid connector, said sleeve distends radially inward to define an opening smaller than said central passage.