My first comp they said it was slightly flat so second comp I did the following and didn't get the same complaint: 1. Using the carb cap I fill really slowly (1 min per 500ml bottle) there is almost no foam apart from the first 5-10ml into the bottle. 2. When the bottle is full I swap the cap to gas and shake for 30 seconds to add extra carbonation to the bottle. 3. Let it sit for 5-10 minutes in the freezer to calm down. 4. Remove the carb cap, squeeze bottle to remove oxygen from top of bottle (displaced when removing the carb cap + dip tube from bottle) and cap with plastic cap. 5. I then shake again to puff the bottle back out (extra C02 added in step 2 was so I could do this).