Replacing black water tank with freshwater tank.

Clamrobot wrote:
My main concern is more about routing new piping from the 2nd FW tank to the sink/bathroom. Would I need a 2nd water pump? Things like that. Thanks everyone for the replies thus far :)

You shouldn't have to route the pipes to the sink/bathroom. They're connected to the existing FW tank.
Just connect the two tanks so the water can flow between both. Depending on how the tanks are situated, you may or may not need a second pump.
You will need a vent on the second tank.