36 CFR § 3.13 - What conditions apply to the use of Marine Sanitation Devices (MSD)?
(b) The owner or operator of any vessel on park fresh water that is equipped with toilet facilities and/or a MSD that is capable of discharge, must lock or otherwise secure the valves or mechanism of the device. Acceptable methods of securing the device include:
(1) Closing the seacock and removing the handle;
(2) Padlocking the seacock in the closed position;
(3) Using a non-releasable wire-tie to hold the seacock in the closed position; or
(4) Locking the door to the space enclosing the toilets with a padlock or door handle key lock.
(c) The superintendent may modify the requirements of this section through a special regulation.