Could you go over exactly how you are using the filler?
While I do not have that exact filler, the use of them should be similar.
After cleaning and sanitizing the bottles, I place the filler in the bottle and allow CO2 into the bottle with the release valve closed. After a short while, I close the CO2 and open the release valve all the way. I repeat this action 2-3 time to try to push out most of the air and replace it with CO2.
I then fill the bottle with CO2, and then close the CO2 line and then open the beer line. I slowly open the release valve to SLOWLY allow the beer to start filling the bottle. Once the bottle is filled, close the beer line and SLOWLY open the beer release valve, until there is not additional pressure in the bottle. You can then remove the wand and place a cap on the bottle.
I prefer to cap on foam. If the foam does not rise to the top of the bottle, I will lightly strike the bottle with a tap wrench or similar to start getting the CO2 to come out of solution. Once the foam is at the top of the bottle, I quickly move to clamp the bottle cap on the bottle.
I hope this helps.
Cheers,
Wayne