There are lots of ways to do it, you can drip some in wait, drip more wait, etc. Or you can use a syringe, or you can drip some in, spin it (taryn spin) drip spin, drip spin, until full. Or you can condom fill. You are looking for the filling to look slushy on top and the center tub clear. Not supposed to put any down the center hole, but not if but when you do blow it out from the battery end into a paper towel. Lots and Lots of videos on you tube showing all the different methods. And counting the drops really doesn't work as different bottle tips have different drop sizes, it really is all about knowing what it "looks" like full.