I started to refill with the mouthpiece down (with or without the white cap), taryn spin, mouthpiece down again, spin again. A good method as long as there is a box of kleenex around.
Then I tried dripping onto the filler, spin, and repeat. I can't really see what I'm doing so I'd lose about two drops per fill.
Only recently I've been experimenting with the battery end down and the white cap off, spin, and repeat. Someone posted it on another thread and I liked the idea of watching the juice soak in, instead of waiting for a drop to come out of the white cap. I'll be refilling about 15 cartos this weekend and then maybe stick with this method for a while.