For a standpipe in an external box, due to space constraints, I would look into the other version of the "quiet" overflow. It's called a Stockman overflow and is on the Durso page as a compact overflow. The only thing I did differently is, instead of drilling holes in the standpipe, I cut a larger square hole at the level I wanted the water to stay. This works quite well and was actually a little quieter than the first one that was drilled per the instructions on the site. It takes up less room than the traditional Durso design and mine is pretty quiet. You can adjust the flow to a degree by inserting a piece of icemaker line into the vent hole at the top. By running the other end of this line down into the stand somewhere, you can quiet the slight gurgling sound even more. Just a thought.