Maybe this will be of some help if you haven't solved your problem yet....
As it seems you only have the problem after filling the kayfun, so maybe you're overfilling it and the pressure created just sends the juice to the chamber, hence leaking and stops faterwards. I have had this problem untill i started to be not so lazy and only fill it untill the transparent section is covered. I wicked the thing more then should be enough but after trial and error i now just fill it until there. Other thing: blow air through the airhole cleaning the tube so you have NO liquid trapped there, this also helps in leaking.
After playing around for a while with it i got the picture and now i can't live without them....
beco
As it seems you only have the problem after filling the kayfun, so maybe you're overfilling it and the pressure created just sends the juice to the chamber, hence leaking and stops faterwards. I have had this problem untill i started to be not so lazy and only fill it untill the transparent section is covered. I wicked the thing more then should be enough but after trial and error i now just fill it until there. Other thing: blow air through the airhole cleaning the tube so you have NO liquid trapped there, this also helps in leaking.
After playing around for a while with it i got the picture and now i can't live without them....
beco