You drip directly onto the atty, unless you have a specific drip tip and then you won't have to take the mouthpiece off every time you need to top off the atty. I don't know much about the Screwdriver 905, but does it typically come with the whistle tip carts? Are the carts filled with the batting? If so, then you'll want to remove that batting if you're going to drip. Otherwise you can moisten the batting filler in the cartridge tip. I prefer direct dripping using a drip tip. Better flavor, better vapor, more
throat hit. I only use the filled carts when on the road. Less hassle than trying to drip and drive.
Also start with only a couple of drops. I'm not sure how much
juice the atties you're using will hold. My standard 510 atties will hold
three drops when bone dry, two when I'm dripping and the flavor tends to fade. Any more than that and it will begin to leak through the ventilation holes where the atty connects to the battery.