46 CFR 35.35-10: -10 Closing of freeing-ports, scuppers, and sea valves—TB/ALL.

The Person in Charge of each transfer of liquid cargo in bulk must ensure that all freeing-ports and scuppers are properly plugged during the transfer except on tank vessels using water for cooling decks. Although under no circumstances may sea valves be secured by locks, the valves must be closed, and lashed or sealed, to indicate that they should not be opened during the transfer.