Unless you do a lot of blue water cruising, do you really need direct overboard discharge AND the ability to dump the tank? As of now, there's no place in your waters where it's legal to do either one, but that's a topic for another discussion.
However...Looking at your drawings...There seems to be a lot more hose than necessary in both your existing and your proposed plan. The vented loop should be immediately ahead of the thru-hull, which would put it AFTER any macerator or manual tank discharge pump.
Here's how I would plumb it: Toilet to y-valve...one side to tank, the other side to the vented loop and thru-hull.
You COULD use a tee or a wye to add the macerator pump, but you'd have to cut into the pumpout line above the top of tank to be able to block flow from the tank to work on the macerator pump. A y-valve might make more sense. That will have to be 1.5" line 'cuz the inlet to the pump is 1.5". However the macerator discharge is 1"...so unless your toilet also has a 1" discharge (making it a Jabsco...every other mfr uses 1.5") and the thru-hull is 1" too, you'll need a reducing adapter to connect the macerator to the thru-hull.
Charlie, your diagram is confusing me. Vented loop usually is a 5/8"hose that goes from top of the holding tank to the deck. You may mean siphone break loop. This hose is also much smaller than deck pump out hose. You can connect the macerator input to the "Y" split off and a 1" throuhull is needed for its output.
You're confusing a vented loop--which IS a siphon break--with a tank vent LINE, Joe.
Peggie