The Subtank has a spring loaded pin, so if enough
juice leaks into the air control base, it will leak out through the 510 connector. I had that happen to me once, and that was because I overprimed the coil and it leaked through the bottom of the coil into the air control base. One or two drops of liquid leaked out through the 510 connector. Luckily I noticed it in time and cleaned it out quickly.