best way to drill my 108?

if it's tempered dont even try it.
It's easier and cheaper to have a local glass shop do it, unless you want to do a lot of tanks.

The bit alone will cost more than what it would to have it done once.

impossible said:

what would be the best way to drill the bottom of my tank(glass 1/2 inch) to accomodate piping for my sump,,,,,is it very risky to do it myself,,,what are the chances that it would crack?

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Have a glass shop do it... and don't do it on the bottom unless you are building an overflow bulkhead around it. Without the bulkhead, you are at higher risk of a leak.

Bear in mind, most glass shops will not even attempt to drill tempered plate.

How old is your tank? You can determine if it is tempered plate or not by using two sheets of polarized filter material and a light source. Tape one sheet of polarized filter to the inside of the tank along with the light source behind it (does not have to be bright), then take the other sheet of polarized filter and put it on the outside of the tank so that you look through it, then the glass, then the taped sheet at the light source, in that order.

Rotate the outside polarized sheet. You should see lines of compression and tension, kind of like contour lines on a topographical map, if the glass plate is tempered.

v/r, N-A

Also, most tanks have a sticker on the bottom center brace that will say either tempered, or all panes tempered.