The drip tip is the standard these days and it serves two purposes. You can add juice through the wide mouth (only good for dripper atomizers, IMO) and it puts more space between you and the atomizer filler. That prevents juice in the mouth, at least most of it unless there's a pool of juice on top of your carto filler. Then, you might get a taste. If you do, then it's time to blow out the carto or atomizer.
Standard cartos are best filled using the condom method, IMO. Tank cartos need a syringe to fill because of the bottom flange, but it's a quick and clean fill.
When the air tube in the center of a carto turns brown, the bottom of the tube is toast and I toss that carto. Cartos were meant for one use only throwaway duty. It's too expensive that way, so we refill them until the taste changes. Some I get 3 days from and others can go as long as a week. It all depends on the juice you vape, the voltage that you vape it at, and how often you top it off. We all get very sensitive about topping off cartos. I carry a 3ml bottle in my pocket for that purpose when I leave the house.
Some people wash their cartos out and reuse them. I've taken enough cartos apart to be wary of extended use. Juice burns in the carto and so does the filler. If they taste funny, 9 times out of 10 you will find burned filler around the coil area at the bottom.
Mine looked like this one. Some were worse. On some, the air tube was burned to the point of disintegration at the bottom and light brown at the top.
http://www.e-cigarette-forum.com/fo...8-4081-etc-filler-type-cartos.html#post301709