Many different types of carts out there. Regular carts,
tank carts, etc. I would repost this and tell us the model you are using. If its just a regular 510, then drip
juice into the open end, on the filler, until it is juicy on top, but not pooling. You may need to use a toothpick or paper clip to move the filler a bit to get air bubbles out, but that's about it. Some pull the filler up about a mm above the top of the cart, but that depends on how big the bridge in the atty is, and YMMV.