If they are prefilled, they are either cartridges that you plug into an atomizer, or cartomizers. If they're cartridges, don't bother. Toss them out and don't waste your juice. If they're cartomizers (one piece), then they can probably be refilled, but you don't want to mix flavors in a cartomizer. Best to get a box or two of empty refillable cartomizers and fill them yourself with juice you buy in bottles. Save your atomizers for testing juices by dripping it straight into the mouth of the atomizer. Get a drip tip to avoid burning your lips. That way, you won't be filling up a cartomizer with a juice you might not even like.