predrilled tank

[Smonkey15]

what does a predrilled tank look like? i thought when i set up my tank that i saw about a 1" circular cut in the glass but now i can't find it. i didn't look much but is this what predrilled means? and if so, why does a predrilled tank eliminate the need for an overflow box to the sump?
steve

 

[scuba_steve]

if you have a hole in the tank the water that is dumped into the tank will flow out the hole that is drilled into the back/bottom instead of over the back and down