A labor extensive means of obtaining "positive segregation" between cargoes would be?

The most effective method for achieving "positive segregation" between cargoes, particularly in the context of tankers, is through the use of a removable spool piece. This component allows the connection between cargo piping systems to be broken and facilitates the removal of potential contaminating connections. By using removable spool pieces, operators can ensure that different cargoes do not mix, which is critical for maintaining cargo integrity and complying with safety regulations.

Options such as piping systems are designed for the transport of cargo but do not inherently provide a means of segregation. Double-hulled tanks focus on safety and environmental protection rather than segregation of different cargo types. Likewise, dedicated cargo tanks do enable some level of segregation due to their design for specific cargo types; however, they do not allow for the flexibility and complete separation achieved with removable spool pieces. Thus, the use of a removable spool piece stands out as an efficient means to accomplish strict positive segregation with minimal labor.