If you look at my photo above you can see the street elbow I used had a small round "knob" (for lack of better terms) sticking up. It is about the size of three dimes stacked up. I set my elbow inside the bucket and marked a line where the top was with a sharpie. Then I put it on the outside and lined up the mark and traced around it. I used a rotozip type tool to cut out the circle. Once I pushed the elbow through the hole I cut out the knob keeps it from going all the way through. When I positioned my second elbow I have them so the backs are touching each other. This will also keep them from being able to be pushed back in from the outside. Once I dumped the feed in the weight of the feed also keeps them from moving. So far so good. Love this feeder. I am not sure if all street elbows have this little raised knob on the top of them or not.