"Holding Tank with Optional Overboard Discharge"

I want something more like "Holding Tank with Multiple Discharge Options" including the "Optional Overboard Discharge" with the Y–valve between the toilet and tank to "upset authorities."

Almost all my sailing is off shore, and with the exception of a few local harbors, (ie Avalon) there are scant few "authorities to get upset."

For Avalon, and other bays/harbors and inside the 3 mile limit, I'd consider cable tie or locking a Y valve to make them happy.

The question I have is do I need to add one more thru hull? Or can I tie the direct discharge line to the tank discharge line to one thru hull. (yet another valve??)

My current system also has a valve (vice vented loop) for incoming seawater... Now I say that with caution, as I saw a vented loop just the other day... I need to go back and trace the plumbing again. (I need to draw out ALL the boat systems, actually)

The other question is for incoming seawater... I know there has been discussion here of using the Lav drain to route fresh water to the toilet to keep things "nice and fresh" at the end of the day. Of course I have the option of just closing the incoming sea valve and using the head shower (on the hand hose) and just rinsing the toilet that way. (hmmm, thinking about it, that seems darn simple enough!)