There are two factors that cause e-juice sucking.
1. The condensate formed by the cooling of the vapor accumulates in the atomizer or the pod, and you will suck them when you vape.
2. There is e-juice accumulation in the coil. In most cases this is caused by insufficient power of the device. Occasionally this happens when you press the fire button but do not vape. E-juice accumulation will not only cause the E-juice sucking, also you will hear the gollum or sizzle sounds when you are vaping.
The solution is that, pull the atomizer or pod downwards to toss out the condensate or the accumulated e-juice, and then use the cotton rod to wipe off the excess e-juice inside and outside the drip tip.
Moreover, if it is a problem of e-juice accumulation, in order to prevent the problem from happening again, remember not to hold down the fire key and not suck, which will not only cause e-juice accumulation, but also burn your coils. If you are using an adjustable MOD, check to see if the power matches the resistance of the coil. Proper power can make the e-juice atomized thoroughly.