Locking the door to the space enclosing the toilets with a padlock...
Apparently you missed "
If you have a treatment MSD (Type I or Type II...) Locking the head door is only acceptable if the toilet is connected to one.
33 CFR 159.7 has the complete list of acceptable means of securing both systems with holding tanks and systems with treatment devices in all NDZs, not just Puget Sound.
Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein