A drip tip is, generally, just a hollow tube with an o-ring at the bottom, that can be inserted into an atomizer or cartomizer (once you remove the atomizer rubber mouth plug). It can simplify refilling a carto (faster to pop out than the rubber mouth plug, though I just left the tip out of the carto), and is necessary on many carto tanks, since the tanks come right up to the top of the carto (not enough carto exposed to put your lips around).