According to your interpretation of the defintion of an MSD, it would be legal
to dump a portapotty overboard
inside the "3 mile limit." I can you assure it's not. Nor is it any more legal to dump a bucket of sewage than it is to dump a holding tank
What you're missing is prohibition against the "discharge" of untreated sewage in all US waters as spelled out in the CFR (Code of Federal Regulations) in several places. The CFR defines “discharge” as "includes, but is not limited to, any spilling, leaking, pumping, pouring, emitting, emptying or dumping." The CFR doesn't limit what kind of device is discharged. Anything that is "INTENDED" to receive, retain or discharge sewage is covered... That can be a bucket or even a coffee cup if that's what you decide to use it for.
See USCG Consumer Fact Sheet #13" for the simplified version:
"Recreational boats are not required to be equipped with a toilet. However, the Clean Water
Act requires that if a toilet is installed, it must be equipped with an operable Marine
Sanitation Device (MSD) that is certified by the Coast Guard (holding tanks
, including portapotties are automatically considered "Certified" by the USCG). Installed toilets that are not equipped with an MSD, and that discharge raw sewage directly over the side, are illegal. Portable toilets or "porta-potties" are not considered installed toilets and are not subject to the MSD regulations
. But they are subject to disposal regulations which prohibit the disposal of raw sewage within territorial waters (3 mile limit), the Great Lakes, or navigable rivers."
However, there is no prohibition against "direct discharge" from you, whether from onboard the vessel (the lee rail is recommended for this) or while in the water
(which accounts for why you may see people with silly looks on their faces hanging on their anchor