Not sure what Grady did with the porta-potty plumbing in '06, but 10 years earlier, this is how it was set up:
A "Y" valve located under a pry-out plate in the compartment under the first step in the cabin directs the flow either to the pump-out port on the port companionway deck - or the mascerator pump under the compartment under the port side helm seat (accessible for repair/replacement by removing the two-drawer compartment). To use the mascerator, you also need to open the seacock at the thruhull in the same general area as the "Y" valve - just below it. To meet CG regulations your "Y" valve is likely zip-tied into the pump-out position, or a lock-out mechanism is necessary.
Some were plumbed only with a pump-out, in which case there is no mascerator switch on your dash panel and no Y valve and everything goes straight to the pump-out port. A vent hose goes through the hull on the port side just under the rub rail.
An '06 hull in great shape likely means your hoses are original, which means it's something to keep an eye (or nose) on....
Good luck and congrats on your recent purchase.
Art