Abstract: Drag modification causes great difficulty for unloading rail tank cars of light oil from upper part. To solve the problem, people tried many unloading methods such as mersible pumps with added low-pressure. Nevertheless, the problem of drag modification hasns't been completely solved. For that, it is pointed out in the paper that the key point in unloading from the bottom part of a rail tank car is the problem of unloading provision's sealing. The two requirements listed below should be considered in order to prevent the fluid from leaking; 1. To provide a sealing ring of required width for the sealing on the contact surface; 2. To provide a counter force (on the sealing ring) higher than the pressure of the medium. Based on the two conditions mentioned above, research is done on sealing of unloading provision installed on lower part of a light oil tank car, with a new type of facility for solving the sealing problem recommended.