Filling this tank is super easy and convenient, the filling hole is inside the tank which can be reached by using a gorilla bottle or just as simply by a glass dropper.
1) Locate your filling bottle/dropper onto the spring loaded filling tube and press it down (only minimal pressure is required).
2) Squeeze the filling bottle/dropper to fill the tank.

Note:
1)After filling, release pressure on the filling tube to allow it to seal, then release pressure on bottle before removing completely, this will draw off any excess e-liquid and avoid spillage directly on to the coil.
2)Due to special design of the tank, after the first filling and when replacing the coil, you should turn the tank upside down for 2 minutes to help saturate the coil with e-liquid.