I empty mine while parked at a dump station, leave the drain valve open, and drive to my storage lot.
My theory is that sloshing around during the drive will get residual water out. But I also have been known to drive the off side tires up on my levelling ramp while parked, to tilt the tank toward the drain and get maximum draining effect that way.
2019 K-2500 Duramax Crew Cab
2014 Silverback 33RL