I also thought about making an algae scrubber from the drain/overflow. In the end, I decided to use the water exiting the skimmer instead. Partly for the flood potential, but mostly because its easier to turn off and either one didn't require any more pumps/power.
Using the skimmer outlet, having back pressure would change the skimmer tuning. So my scrubber is just mounted into a 2" pvc pipe with a hole drilled into it. The water from the skimmer just falls into the hole and if it gets clogged at all, it just runs over the outside of the pvc and falls in the same spot it was going anyway. I made my sump and designed in a spot for filter floss that this drains on. It catches any algae that breaks off and the filter floss is really quiet.
Its fine even with the scrubber completely removed.
Using the skimmer outlet, having back pressure would change the skimmer tuning. So my scrubber is just mounted into a 2" pvc pipe with a hole drilled into it. The water from the skimmer just falls into the hole and if it gets clogged at all, it just runs over the outside of the pvc and falls in the same spot it was going anyway. I made my sump and designed in a spot for filter floss that this drains on. It catches any algae that breaks off and the filter floss is really quiet.
Its fine even with the scrubber completely removed.