I was at the end of a vial. Didn't know how much was left, but figured it was not a full dose. My wife, a former medical assistant, used the syringe properly to drain the vial. It turned out to only be about 10 units. So she got the rest, another 50 units, out of a new vial, into the same syringe for the shot.
It didn't save much, but it was easy the way she did it. I fumble with those syringes. I thought I had gotten the full 60 units out of the nearly done vial, but turned out I shot myself with air but didn't know it. Needless to say, that was a disaster.
The trick, so she told me, is to insert the needle into the upside-down vial, just a little to get what is at the bottom. Sounds easy, but not for me.
ED started in late 30s with vasectomy, but doctors swear that wouldn't do it. Used Viagra, Levitra with mixed results. Started with bimix; now injecting trimix at age 59.