Cutting Holes

[M1i1t1c1h1]

I am in need of some advice regarding cutting holes for my overflow.
Unfortunately due to the fact that my tank is secondhand, I have really no good way of knowing if the glass is tempered or not. There is already an existing hole that was likely not manufactured (and drilled by a previous owner). It looks as if the hole has some defects around where it was drilled.
I see no stamp or label that states whether it is tempered or not. The advice on other forums state to knock on the glass and hear the pitch. Unfortunately I have no basis of comparison so that does nothing for me. I am reluctant to drill into it without concrete proof that it is not tempered.
If I do find out that it is tempered, how do I go about cutting out the necessary holes?

 

[andrewey]

Lol, "the pitch". You can dismiss that advice off the bat.

Do you have any polarized sun glasses?

 

[M1i1t1c1h1]

Lol, "the pitch". You can dismiss that advice off the bat.

Do you have any polarized sun glasses?

I do not unfortunately =/ I saw that people suggested that as well, however I don't even own sunglasses lol

 

[homer1475]

Plenty of videos on youtube(looked myself a little while back) on how to tell. From using polarized sunglasses(they were like 5$ at the gas station), to other ways. I found the sunglass's, and cell phone trick worked quite well.

 

[jdiefenbaugh]

Plenty of videos on youtube(looked myself a little while back) on how to tell. From using polarized sunglasses(they were like 5$ at the gas station), to other ways. I found the sunglass's, and cell phone trick worked quite well.

I would 2nd all of this.

As for your existing hole, you're always going to get some amount of tear out when the bit pops through. I prefer to drill from the inside-out if at all possible because of this. If you were to get a large scallop of glass to come off with the hole, the bulkhead gasket may not seal as well.

 

[M1i1t1c1h1]

Plenty of videos on youtube(looked myself a little while back) on how to tell. From using polarized sunglasses(they were like 5$ at the gas station), to other ways. I found the sunglass's, and cell phone trick worked quite well.

I don't think I've heard about the cell phone trick... What is that one?

 

[DeniseAndy]

Most tanks are tempered on the bottom only. However, I would try the tricks to see too.

 

[mijan]

I don't think I've heard about the cell phone trick... What is that one?

Place the cell phone on one side of the glass. Make sure the phone is lit with a white screen. On the other side of the glass look through your polarized lens at the white screen. Rotate the polarized lens. if the screen turns black through the lens it's regular glass.

 

[M1i1t1c1h1]

Place the cell phone on one side of the glass. Make sure the phone is lit with a white screen. On the other side of the glass look through your polarized lens at the white screen. Rotate the polarized lens. if the screen turns black through the lens it's regular glass.

Thanks! I will give this a shot