Pollution Laws are state based. In Queensland
the Transport Operations Marine Pollution Act
and the Regulation
Short story is that if you have a fixed toilet, you must have a holding (or treating) system if the boat is in nil discharge waters.
Nil Discharge Waters means:
Prohibited discharge waters.
If a ship has 16 or more persons on board—Hervey Bay waters, northern Moreton Bay waters and open waters.
Hervey Bay waters and northern Moreton Bay waters, within 1852m of any of the following—
(a) aquaculture fisheries resources;
(b) a reef;
(c) the mean low water mark of the mainland.
(a) within 926m of a wharf or jetty other than a jetty that is a marina; or
(b) within 1852m of aquaculture fisheries resources; or
(c) if a ship has 7 to 15 persons on board—within 1852m of any of the following—
(i) a reef;
(ii) the mean low water mark of an island or the mainland.
Prohibited Discharge waters means
prohibited discharge waters means waters of any of the following—
(a) a boat harbour; (b) a canal; (c) a marina; (d) a designated area.
A designated area means
- well great lumps of the planet, certainly almost any where you want to be.
Also - even where you can discharge you need to have untreated sewerage run through a macerator.