Never heard of gray water discharge restrictions in the Florida Keys National Marine Sanctuary and not even in the Ecological Reserves around the Tortugas. Gray water discharge has been recognized as an exception to the general ban in a similar way as as cooling water discharge. I have not heard that has changed. This in no way conflicts with sound ecological recommendations from the Park Service personnel. Holding gray water in the boat's bilge will promote bacteria growth and negate a safety concern for the boat. Be consious, limit the use of soaps and detergent and strain solid food particles. Solid garbage as well as sewage is unlawful to discharge. Become familiar with access, anchoring and fishing restriction.
Nevertheless, as a practical matter, ask the Marine Patrol Officers on site what are the restrictions and live by their interpretation.