There's a damper assembly in the fork tube, it's about 12-14 inches long, and is held in place with a bolt on the bottom of the fork tube, that's what prevents the rod from going all the way down .
Is the fill port bolt installed ?
Did you drain out the original oil before adding the new oil ?
If it is, that would prevent oil from draining out, if the bolt is out, you need to put a small diameter tool, like an allen wrench into the drain hole opening .
It's pretty common to have a rubber bump stop deteriorate, and clog up the drain .