When you get to near the end of a vial, it is not possible to get all of the genie out of the bottle.
I found something that works. A specific example that you can adapt.
Watson’s T cyp has a rubber stopper that is dimpled on the inside to facilitate removal, but you can’t see where the end of the needle is in there. I removed the stopper and measured the thickness that the needle goes through. I use Walmart/Sam’s house brand “relion” #29 .5" .5ml insulin syringes to inject my T EOD.
I cut back one of the needle caps to expose just enough needle to partly expose the taper at the end of the needle through that stopper. I ended up with the orange cap to 5/8" [0.64" or 16mm]. With that cap on, it is possible to have the needle inserted into the rubber stopper to the correct length to remove most of the T.
I keep that cap in my kit bag.