How can I get my hummingbird feeders to work?

Question

I have several hummingbird feeders that give access via a red rubber plug at the end of slightly bent glass tube. The tube fills about 50% with nector and then there is a big air bubble. After the birds drink the nector in the tube, the bubble prevents more nector from flowing down. How do I overcome this?

Answer 1

If they are all like this could it be a design defect where they simply don't work?