I had the same problem when I started my 110g. I had to make my own overflow from a hang overflow box since my tank is glass. I just took a long 1/4 in diam. tubing(found at most hardware stores by plumbing dept.) and cut it long enough to go from the overflow all the way down under the tank. The key is to get the tube positioned at the right depth in the overflow box down pipe that goes down to your sump. You may have to adjust a couple of times.
A couple of things to remember. The tube you use should be as big as you can without restricting the flow down to much. If it is, use a smaller hose. This is the cheapest way to get rid of the gurgaling sound that bothered me. If you have the room, use the durso set up.(make your own, don't buy) Otherwise use the tube. Simple, effective and cheap, my favorite way. Hope it helps.
