Hold the rod up for easier filling. Start out with about a 1/4 qt. Then pump the cartridge, it will drop level quickly as the air is removed from inside the cartridge.
Just a bonus shot
Install Seal seat.
Install seal, PN face you as your pressing them in.
Install seal retaining ring, press it into the groove and work it around. If its not in the groove the seal is not fully seated.
Install Dust wiper, simply press into fully seated position.
Installed view, lube the wiper and seal inside surface to prevent seal damage during assemby.
Carefully slide upper tube over lower tube, and work its way down to the fully seated position. If there is any resistance you may have a bent fork (this was the case on this particular fork set).
Go ahead and fill with fork oil. Once full, pump the cartridge rod about 10 times, and then let sit a few minutes to ensure all air is out of the system. After that you triple check fluid level, and make sure its full.