First, take a look at the bottom of the tube...to see if it has suctioned itself to the bottom or side of the bottle. If needed, snip an edge of the tubing off at an angle...so it makes and inverted V or U...that way it will never suction itself against the bottle again.
Next... You may want to try to see if there is blockage inside...I do this by removing the bottle..., hold my finger lightly over the end of the tube, and put the catch cup in my mouth and blow. If air is getting through, then there isn't any blockage.
If there is blockage, run the end of a paper clip down the feed hole in the connector gently. There shouldn't be anything in there, but you never know.
If you're using a thicker juice, sometimes the first feeding is the most difficult. Once it gets going, it should be fine. Let us know what you find.
