Under the federal regulations of 33CFR Subchapter O, if a vessel equipped with a Type II Marine Sanitation Device enters a body of water where the discharge of treated or untreated sewage is prohibited, which of the following methods of securing the device to prevent the discharge of sewage is ACCEPTABLE if it is impractical to close the seacock and prevent its opening?

Correct Answer: Option D — Locking the door to the space enclosing the toilets with a padlock or door handle key lock to prevent entry when the vessel is entering a "no discharge zone".

33 CFR requires that Marine Sanitation Devices be secured to prevent illegal discharge in restricted waters. When closing the seacock is impractical, locking the toilet space prevents usage, effectively securing the system. This physical barrier ensures compliance with environmental regulations by preventing the introduction of sewage into the prohibited area.