Originally Posted by wolfenzee
I believe the laws refer to "raw" sewage, I would check into the legality of dumping composted sewage, but it should be legal.
The Coast Guard regulations cover three types of MSDs. Large vessels use either Type II or Type III MSDs. In Type II MSDs, the waste is either chemically or biologically treated prior to discharge and must meet limits of no more than 200 fecal coliforms per 100 milliliters and no more than 150 milligrams per liter of suspended solids. Type III MSDs store wastes and do not treat them; the waste is pumped out later
Section 312 of the Clean Water Act, which is also known as the Federal Water Pollution Control Act of 1956, requires a certified operable MSD on every vessel with an installed toilet to prevent the discharge of untreated or inadequately treated sewage into U.S. waters.
A properly functioning composting head would fall under the catagory of a Type II MSD. Though it is not being "discarded" because it does not go through a through hull.
The problem is that the unit needs to be coastguard certified
as a type II MSD. I asked about this with the designer of the Nature's head. Both the Nature's head and Airhead are type III, which is the same as a portapotty as far as the USCG is concerned. You can't (legally) dump the contents of a type III overboard within US waters.
Also, the Nature's head and Airhead don't compost the fecal matter to a safer level than fresh fecal matter. Mostly they store and dry it. In order to safely compost human manure it must be composted at high temperature. See also: "thermophilic composting". For further reading I HIGHLY recommend "The Humanure Handbook."