drilling back side of tank??

[Orion80]

I just bought a oceanic aquarium model 75E (Glass) and it does have the temperd glass bottom, is it possible to drill the back plate, and if so would it b best to drill it at the bottom just like u would normally drill or would u set up the hole at the top for your overflow????

Any help would b appreciated, would really like to get rid of my external overflow...

Adolph