A Monte Carlo method was used to calculate the probability that a molecule passes through a cylindrical tube with wall sorption. This probability is presented as a function of the ratio of length to radius and the sticking coefficient s of the wall. For s=0, the results confirm those of Clausing for the conductance of a tube of finite length. For s≠0, wall pumping can greatly reduce the flow of gas, even for very small values of s. The backscattering, total flux retained by the wall, and its distribution along the tube also are presented. Finally, the collimation of the emerging beam is investigated.