. . . "Additionally, the flow tube 1910, which is preferably constructed of a relatively hard material such as ceramic, tungsten carbide, or PDC, is relatively thin (i.e., has a low thickness, as measured from an outer diameter to an inner diameter of the flow tube 1910) to facilitate drillability of the flow tube 1910 when a cutting structure, such as an earth removal member attached to a casing or a dr" .