Some thoughts:
No drilling
If, for example, you are mounting the external pump to the stand. just use PVC piping, elbows etc... to extend the pump intake down into the sump.
Drilling
Some people plumb their systems as though a leak could never develop so in theory you can drill the sump anywhere you want (within reason) but the closer to the top - the less volume lost should a leak develop between the bulkhead and the glass. If you want to draw water from the bottom of the sump this can be achieved by using PVC fittings on the inside of the sump.
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RM250