Sump question

[Treebeard]

I am planning on building a sump from a 20 gallon glass tank. The current setup consists of a 46 gallon bf tank, Seaclone protein skimmer and an Eheim 2026 canister filter. I will put the skimmer in the sump, but I am not sure what to do with the filter, or even if I really need it? Should I run the filter in the sump?

Any other advice before I start this job would be greatly appreciated!