Thanks, Karch.
I assumed the bottom of the hole was the proper level, but I could not find a confirmation.
I recently acquired a 30K mile takeoff blower & I wanted to be sure it wasn't drained or tampered with.
I heard it held 6oz, so I picked up two 4oz bottles.
When I drained it, the level was at the bottom of the fill port & a measured 4oz came out, so I refilled it to the same level.
The cover was not removed, I only dumped it out through the fill plug. Since it was so clean, I did not feel the need to pull the cover. Not sure how 2 oz supposedly stayed in there. I even spun it for a while & rechecked it because I was paranoid about the missing 2 oz.