When you swivel the top back, look at the U shaped fill port. There can be a juice film in that port that creates a airlock when your filling it, you either blow down or use a wipe of some sort and remove that film. Sticking your jug tip doesn't always break that film and when your filling the air has nowhere to go but force the juice out the bottom. Same concept as filling my TFV4 and since I figured out that the film was my problem, I never close the airflow and it doesn't leak after I fill it.