I have full flap set at 85 degrees which seems to do the job without crow. Others may feel differently.

I simply hook the feed line on my taxi tank to the vent line coming from the main tank before I start to fill the plane. When the plane is full, the taxi tank will begin to fill. Stop the fill when you have what you think you need in the taxi tank. Everything on the plane is completely full and nothing spills on the ground. My fill line comes from the UAT.