A dripstick is a thin hollow tube installed vertically in the bottoms of fuel tanks of many large aircraft, used to check fuel levels. To read a dripstick, it is withdrawn from the lower surface of the wing. When the top of the dripstick is withdrawn below the level of the fuel, fuel enters the dripstick and drips through a hole in the cap. Graduations on the dripstick indicate the level of the fuel in the tank.
Newer aircraft use a floatstick.
References
Dripstick Wikipedia(Text) CC BY-SA