bubbles coming out of gas line

When I attached a hose to my fuel rail to remove some gasoline from the tank (by turning on the in-tank fuel pump), gas comes out in a strong clear stream. When I turn off the pump, gas continues to come out by syphon action (although flow is much less of course) but with a steady stream of bubbles. Where are they coming from? The car is a 1995 Geo Tracker with the 4 cyl. 16 valve engine. No fuel leaks and everything in perfect working order.