I was going to do something similar. My fresh tank is on the right side along with the water pump, and my grey tank is on the left side.
The sink for sure had to go on the left, and I only had space for one tank per side. So I had to decide which side would be fresh and grey.
I opted to make the right side (opposite of the sink) fresh, and just plumb the pressurized PEX tube across to the left. Originally, I was going to go under the bus like what you're saying, but then I decided to just plumb it through the rigid insulation of the floor.
I figured I'd rather have the pressurized water go across as opposed to draining, because like what others are saying, the slope can getcha, and I didn't want the potential for any blockage halfway across. So the sink just drains straight down into the grey tank.
I HIGHLY recommend the Hepvo fitting, I think PNW Steve originally clued me in to that great contraption. It saves a lot of space and just make things easier.