Originally Posted by MedSailor
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."
Anything which doesn't discharge overboard is legal, as it is none of the coast guard's business, if it doesn't enter the ocean..