Using this gets rid of the yucky wadding! It wicks a lot better than the stuff that comes with the carts and there is no horrible burnt plastic taste when it gets a bit dry.
This is standard solder wick used to soak up excess solder from a joint.

Cut off 5cm

Tease it out to around 5mm width

Fold it in a zigzag

Use a small screwdriver to push it in the cartridge

Make a small gap at the side for air to surface while filling.

This one took 12 drops of liquid.