Usually, these symptoms are user error. Your juice attachment, or tank, sounds like it is "flooded". E-liquid drops in the mouth while vaping is known as "spit back".
Flooding is a common occurrence in e-cigarettes. The definition of flooding is getting juice into the air passage of the tank. This can include any point between the mouth piece and the very bottom part that connects to the battery. Each tank has holes in that air passage, where the wick passes through. This is required for the device to work properly. Unfortunately, this opens up the possibility for flooding. The trick with flooding, is knowing how to avoid it. I’ll explain a little more, but a few common causes for flooding a tank include: improper filling, over filling, pulling too hard when hitting the device, and the temperature can even play a role and/or damage.
Before I get into the explanation, let me explain how an e-cig works a little more in depth. Nearly every tank has a wick that is used to absorb the juice in the tank. This wick cuts through the air passage. Typically, the wicks looks like a wad of cotton hanging in the tank. Each wick has a piece of wire that wraps around it in a coil. When you activate the button on the battery, you send electricity through the wire. As the wire heats up, it vaporizes the juice that is in the wick.
Improper Filling: When filling your tank, you have to be careful not to get juice into the center tube of the tank. This center tube is the air passage. When you take a draw, air comes from the bottom of the tank, through the air passage and into your mouth. If you get juice into this passage way, your tank is flooded. Be sure to add your e-liquid into the space outside of the center air tube.
Over Filling: If you over fill a tank (specifically a top coil like the ones that come with the starter kits and gift boxes), the wicks can become over saturated and just like a rain cloud, they will leak into the air passage. Once this happens, you have a flooded tank. Most tanks have a maximum fill line marked.
Pulling Too Hard: This seems to be the most common culprit for flooding. As I mentioned the wicks absorb the juice in the tank. As you pull on the device, you cause a vacuum effect that pulls juice into the wicks. If you pull too hard, you can pull in more juice then the coil can vaporize. If this happens, the juice leaks into the air passage and you have a flooded tank. Use a more gentle draw when you vape.
Temperature: E-Juice is a viscous liquid. Which means that as it warms up, it will thin out. And in the opposite form, it will thicken when it gets cold. When it thins, it is more difficult for the wicks to hold back the thin juice. This usually causes the wicks to over saturate and, you guessed it, it will leak into the air passage and you have a flooded tank. Heat generally makes liquids expand in volume, and the liquid will seek out the path of least resistance (center air tube or the air intake hole).
Damage: There are o-rings and gaskets used that can wear out with usage. If certain ones fail or get lost, leaking will occur, in turn flooding the air passage and causing you to have a flooded tank. Other than accidentally losing something, damage can occur when its carried in a purse or a pocket or by over tightening the tank to the battery. Over tightening is a very common cause of leaking due to the damage it creates. A micro crack in the glass will also cause leaking.
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It's not unusual for the tank and drip tip to feel warm, or even hot to touch, especially if you hit the fire button frequently. After all, the tank has the heating coil in it, and that coil can get pretty hot in order to vaporize your e-liquid. The heat is easily transferred to the drip tip.
I can't offer any specific places to find e-liquid. You didn't include where you are located.