I've never seen or had this weird a setup on my boat or any of the ones I've worked on thus far.
Have no idea why you would want to flush the head using the holding tank contents... EWWW...
The setup on my boat is that you can use the contents of the head SINK to flush the head.... not the holding tank. That allows you to use fresh water rather than salt water to flush the head—which can be better if you're leaving the boat for a while, since it won't have the micro-organisms that salt water has—which eventually die and stink up the head compartment. It also makes it pretty simple to winterize the system.
The simplest setup is usually the best when it comes to the head IMHO. I would recommend that you plumb the head output directly into the holding tank. Then plumb the output of the holding tank to a diverter valve (use the one from the head output that you'll be removing) that leads to either the deck pumpout fitting or the macerator pimp and then to the discharge seacock and through-hull.
The macerator pump should be after the diverter valve, since that will prevent the deck pumpout from pulling waste through the macerator when it isn't operating—which could clog or damage the macerator. It also prevents you from having the macerator pump pushing waste up to the deck pumpout fitting section of the hose and pressurizing it... which can lead to a really nasty surprise to the next person opening the deck fitting.
This way, you can empty the holding tank when out past the three-mile limit, or via a pumpout boat/station. You're really not losing much in the way of capability, since any time you'd normally discharge the head directly overboard, you can always discharge the holding tank overboard instead.
You'll probably want a lockable diverter valve, since the authorities prefer to see one that is locked when you're in an NDZ.
I hope this helps.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.
—Cpt. Mal Reynolds, Serenity (edited)
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