This might be a better question to ask on the Jester Challenge Yahoo forum. Pete Sutherland is the moderator and as a US citizen [upper NY State resident] he can probably give the definitive answer.
My understanding is that a holding tank is required for black water, but I am unsure of grey water. Anywhere within the US 12 mile limit blackwater should not be discharged. You either discharge at a station at most marinas or go beyond the 12 mile limit to discharge.
The easy answer for small boat owners that don't want to fit a holding tank is to have a porta potty.
While I was in Newport Harbour I did dump urine over the side but went ashore to defecate - The Seaman's Mission has excellent facilities and does a good breakfast too.