possible to turn over flow into power filter?

My stand is a cheapo steel stand that holds two tanks a 20gal on top and a 10 gal on the bottom. Currently I have the mantis tank on the top sitting on a piece of plywood draining into another 10 refugium on the bottom.

My intention is to remove the refugium move the mantis tank to the bottom and put a 20 gal on top for a different mantis. Only problem is the mantis tank is drilled with nothing for it drain into.

So my plan was to plumb the over flow into a external pump and put a filter pad across the over flow. Would this work to create a cheap power filter of sorts?

I don't really know what else to do with the over flow so that I won't have to remove it and it won't trap debris. I could switch tanks but that would require stirring up the sand bed. Which is only about 1.5" so not deep by any means but I'd still like to avoid it if possible.

 

I don't see why you couldn't do that although that sounds like an expensive option and a lot of extra work and maintenance for something that is essentially just mechanical filtration which I'm skeptical of anyway.

You could just plug up the overflow bulkhead. I believe there are bulkhead "blanks" (I think that's what they're called anyway, maybe I'm wrong) which will fit where a bulkhead is but they just plug it up, they have no hole for plumbing.
Or you could just stick a short piece of PVC in the bulkhead and cap it off.
I don't know how much junk would actually collect in the overflow without water actually running through it. It should be pretty easy to clean out though I would think. Or you could just keep the water level below the overflow teeth so the overflow stays dry maybe?

Maybe you could figure a way to plumb the two tanks together? Greater water volume, more stability, easier maintenance for water changes etc.
Drill the other mantis tank and put an overflow on it and use an external pump on that one but pump the water up to the top mantis tank which would then overflow to the bottom one and then back to the pump.
It would be like the mantis on the bottom is living in the sump but the external pump would make it a display tank as well. I don't know how that would actually work out, just trying to get creative with the problem.