I hook the bottle full of water up to the soda stream, press the button to shoot in carbonation, and the carbonation just shoots out because the seal isn't airt

I hook the bottle full of water up to the soda stream, press the button to shoot in carbonation, and the carbonation just shoots out because the seal isn't airtight. I've tried pressing it short and quick, long and hard, etc. I just can't seem to get it to carbonate properly. Thoughts?