What is residual fuel and oil described as?

Residual fuel and oil are characterized as a fluid that is trapped in the lines and cannot be drained out. This refers to the tendency of these substances to remain in the fuel lines, tanks, or other areas of the fuel and lubrication systems even after an attempt to drain them. This trapped fluid can lead to contamination issues and reduced efficiency, as any residual substances can impact the performance of the engine and its components. Knowing that residual fuel and oil can accumulate in inaccessible parts of the system highlights the importance of proper maintenance and procedures to avoid potential problems during engine operation.