I came up with another use for this. I have a go-go, and I had loaded one of the 3 ml cartos with a flavor before testing it in a smaller volume. Turns out I wanted to add some sweetener to it, and I was mad that I'd wasted 3 ml on a carto and didn't want to
vape it.
I put the carto open side down into a 15 ml conical centrifuge tube and capped the tube.
Then I spun the tube and carto in a sock. The centrifuge tube caught the
juice as it was slung out of the carto. I had to repeat it 3x to get all the
juice out, but it allowed me to save most of the 3 ml and add it back to the bottle so I could sweeten it.
Just thought I'd mention that here in case anyone else ever ran into that situation. Probably everyone else is smarter than I am and doesn't load a 3 ml carto with an untested juice