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 C — 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".

When a vessel enters a no-discharge zone and cannot close the seacock, 33 CFR 159.7 allows securing the device by locking the toilet space. This prevents the use of the system entirely, ensuring that no sewage is generated or discharged while the vessel is within the restricted area.