I just remove the 3ml bottle top -fill the bottle from whatever juice bottle I'm currently using - stick the needle top back on the 3ml bottle and put back in the OG.
As far as the leak, it's hard to be specific. Perhaps ur squeezing more than needed and it's running back down. Make sure the 3ml bottle top is on properly. I've had mine for about 4 months and don't have the newer style drip cup. Sometimes when I use cartomizers, I've seen juice leaking from my carto, which just means I filled the carto too full.
As far as the leak, it's hard to be specific. Perhaps ur squeezing more than needed and it's running back down. Make sure the 3ml bottle top is on properly. I've had mine for about 4 months and don't have the newer style drip cup. Sometimes when I use cartomizers, I've seen juice leaking from my carto, which just means I filled the carto too full.