As you can see, it is in sump. I tried running it external, but there was some leaks where I connected the tube to the inflow pvc, so I run it in sump. You can run it external as long as you is a bunch of pvc cement to attach the metric pvc to standard parts.
There were no instructions either on mine, mmedley, so I imitated, ok, ripped off the design ---- sellers are using for this skimmer.
The body is milked almost all the way to the base, and there are no microbubbles flowing out of the overflow tube, either.