30 to 35 drops! Wow, you are the king, have no clue how you can do that? I agree about not letting the carto get dry. The moment my flavor starts tasting funky, that's when I stop.
I throw that carto in my plastic bag full of almost empty carto's and move onto the next new or refilled one.
The carto's which are almost empty or dry, I'll either refill them (top them off in reality) or I'll boil and dry them. I check the inside to see if they're alright then refill them. At most on a new or a clean carto I can get about 20-25 drops in.
If I let the carto sit for a few minutes, then roll them in the palm of my hands, I find I can add more juice...that's when I can get up to 25, with any luck 28 drops in.