Phiniac sells the tank tool designed and manufactured by Siam Mods. I have that one and found that I liked the skinnier tools like the ones below. The Phiniac does what it was designed to do, but you will have to pull the carto down farther during juice refills than you will with the below tools. They allow more open space to add liquid without having to pull the carto so far in the tank.
I also found that this tool can be difficult to remove from the cartomizer when its time to replace it with drip tip; it fits far too snug than it needs to.

Above is the less expensive delrin version of the Slap Yo Moma. It works exactly like the more expensive SS version. The second tank tool above is the one that IBTanked sells for around $3, and it works well, too.
Both of these provide plenty of room to add e-liquid to the tank, and are easier to remove.