Paper deals with the problem of marine pollution resulting from oil tankers in service when the decision made is in favor of legislation or financial savings. When the crew on completion of cargo transfer operations, comes to the cargo tanks - tank washing, tank washing waters are collected on ship. Management of tank washing waters, according to the position of the ship has several possible solutions. In coastal zones, straits, bays, and special areas where tank washing water is not allowed discharging overboard, there are three options: • be discharged ashore (see Fig. 1), paying for the service; • be kept on board, where it is always not enough space; In this situation, the crew is forced to compromise between the existing legislation, environmental pollution problems and the charter of the vessel and company requirements.