I had a 155gal bow front that was drilled in the back. The overflow were only 6" x 6" so I took a 90 degree elbow and cut it as shrt as possible on one end then made a took a very short piece of 1 1/2" PVC pipe glued it into the elbow and shoved it into the bulkhead but did not glue it. The top end was a Hofer Gurgle Buster. It was compact, easy to build and adjustable.
Just another idea to add to the rest
