Does the port charge container owners for storing empties? Ramp up the storage fee, and voila... empty containers go back on empty boats that would otherwise make the return trip with no load. Container owners will find that shipping them back with a reasonable premium to keep ships around long enough to pick up the empties eventually costs less than storing them at the port.
Aside, I'd love to have an empty container on my parcel out in the desert, if there's such a huge glut of empties, why does one in any condition cost $10k, without delivery? If anyone has a source for empty containers for sale at reasonable prices, I'd love to have their contact info.