Mod SWC 120 Cone to be Recirculating?

[sphelps]

Recirculating mod would be easy although probably not all that beneficial.

However if the goal here is to use this skimmer externally sealing it properly will probably not be that feasible. If this is the goal I'd suggest building a small tank with overflow that the skimmer just fits into, then pump water from the sump to this tank and allow it to overflow back to the sump. Effectively you've created a recirculating and external skimmer without actually modding the skimmer itself. This is something I can help you with if you'd like.