A single 1" drain is good for ~600gph and a 1.5" for around 1200gph (remembering if planning a Herbie, the second drain is normally dry and only flows in the emergency situation).
If doing a Herbie, me, I'd go 1" return and considering it's a 45g, probably just 2x1" drains if not planning on your return pump contributing significantly to the displays flow. 2x1.5" if you don't mind a bit of flow through your sump.
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