I just got a couple of cans of $2 degreaser from Supercheap Auto, used them on it, then rinsed it off with our pressure washer. It came up lovely! I think just rinsing it off with a hose after using the degreaser would probably do a fairly good job too.
The only places I tried to keep away from while washing were where the flexible hoses connect into the rack.
Good luck. Its a fairly easy job!