I've had hard draw, for two reasons so far.
One reasons seems to be
juice blocking the passage somehow.... i unscrew it from battery, blow through it really hard, problem gone. Has happened two times in three days.
Other reason is the sleeve between battery and tank was too tight to the tank, or mis-aligned, or something, i screwed it tight to the battery and problem was solved.
Could be that one or the other above was the problem all three times, and i stumbled upon the fix somehow (can't blow it out without unscrewing, and can't unscrew without bouncing it around a bit).