Take them apart, only way to get the crud out, it all collects at the bottom right on the base valving.
Yes, the oil level is set with the springs out and the forks collapsed
Note, when turning the forks upside down to initially drain the oil be careful not to loose the rebound adjusting needle and spring. This item is "captured" in most late model forks but not the DRZ Showas. The spring and needle "lives" in the piston rod. The last set I did the customer previously changed the oil himself, when I received the forks the rebound adjuster needle and spring were MIA!! :scream:
Good Luck, Vet