I found out that my positioning and the strength of my milk flow caused that to happen occasionally. I could not prevent it, but I did clean out my tubing in the Medela steam bags which always worked.
Directly after pumping I would let the pump stay on and let the tubes stay on too, while I carefully took care of my milk. Then what I did was turn the pump off and take the tubes and swing them around my head rodeo style and that got rid of the condensation that builds up as well.
