I have no bubbles in the sump at all, i do have a wall in between the sock and the skimmer but there is no bubbles that come from the sock, yes the sock is right below the drain line from the overflow , i have 2 -1 " lines from the overflow box. you can call World of Fish @ 612-866-2026 , they said there just a bag hanger filter sock that they sell in bulk , they are made of a thick material, you could make one out of a filter material that you would buy bulk and sew one together in the form of a sock to fit ur sump, this sock i bought was about $ 10.00 very cheep to buy rather then make.