A little understood info about gurgling and topping up.
While I rarely get any type of gurgling, I can understand it happening to some over time.
Condensation can and does build up in the tube.
This starts to restrict air flow.
Restricted air flow reduces draw and leaves even more condensation in the tube.
Eventually these condensation droplets pool and slide down the tube. Now you have a Gurgle and a small puddle of liquid. Not much of that is actually e-liquid, it is mostly water with some flavoring mixed in.
So, why does topping help?
Some believe it is because the tank needs air back inside.........Umm, nope. Lack of Air would help prevent excess flow of liquid.
While Topping, The Base/coil is off.
Mose people wipe off the spillage/goop/excess that runs off the coil/base while re-filling. Remember where the accumulated condensation goes?(DOWN)
Occasionally while re-filling, the Tank is sitting on the mouth piece. It is not uncommon to have a small liquid puddle where it was sitting and that gets wiped up to.(More condensation)
Hers is where a Q-tip should be used to dry the inside of the mouth piece before turning upright.
Breathing through your power release, continuing the draw for 1/2 second can reduce condensation by more than 50% possible higher.
This will significantly reduce build up in the tube over time.
Think about it