All the experts say not to connect a raw water
flush toilet to your pressure fresh water system. They say there is danger
of contaminating your fresh water supply.
On toilets designed to flush with fresh water, Jabsco uses a solenoid valve (37038-1012 or 37038-1024) with syphon breaker to control the intake water. You could probably by pass the intake pump and install the solenoid valve in the fresh water supply line and run a hose to the back of the bowl from discharge side of the solenoid valve. Then you'd need to figure out the wiring
and control. Talk to Jabsco about this before you do it. There may be other dangers that I don't see.
Another option would be to install a tank that holds water that will only be used to flush the toilet and make sure the two systems are never connected together.