Final answer:
The 'Y' valve on a Type I or Type II Marine Sanitation Device must be secured to ensure sewage is treated and not discharged directly into prohibited waters, thus the statement is true.
Step-by-step explanation:
When discussing the 'Y' value on a Marine Sanitation Device (MSD), it refers to the Y-valve which directs waste. In maritime environmental compliance, Type I and Type II MSDs are designed to treat sewage before it is discharged into the water. According to environmental regulations, particularly the Clean Water Act and the regulations set by the U.S. Coast Guard, the 'Y' valve must be secured in a closed position when a vessel is operating in waters where discharge is prohibited to ensure that sewage goes to the MSD for treatment, and not directly overboard. This is typically enforced by using a lock or a non-releasable wire tie.
So, to answer the question, it is true that the 'Y' value must be secured to direct waste to the MSD and not to the environment. Not following this procedure can result in legal penalties and environmental damage.