I raised the skimmer output above the water line in my sump. I then took a 1 Gallon water/milk type jug, and cut a hole on the side, and one on the bottom. I place the output of the skimmer on the hole on top, and the put the hole on the bottom below the water surface. I tied the whole thing to the stage I placed the skimmer on with airline tubing.
This was a spur of the moment idea to deal with a frustrating problem, and has worked so well I haven't devised a better solution. It has been in place for about 3 months, and no bubbles enter my tank.
My sump is in my basement, so I have the luxery of lots of room to raise the skimmer.
I would recommend baffeling your sump if you do not have the luxery of height.
This was a spur of the moment idea to deal with a frustrating problem, and has worked so well I haven't devised a better solution. It has been in place for about 3 months, and no bubbles enter my tank.
My sump is in my basement, so I have the luxery of lots of room to raise the skimmer.
I would recommend baffeling your sump if you do not have the luxery of height.