Drilling is so easy it isn't true. Trust me. It is also less likely to fail (which is why I always go drilled).
I see you are in the UK, so the chances are the tank won't be made from tempered glass. If you are worried about tempered glass, just drill the back and use a mini weir rather than a bottom hole and full weir.
All you need to do is buy a proper glass drill bit. I think I got mine from Lau superstore or something, either way I paid a total of about £12 for two drill bits for 25mm bulkheads (so around 35mm) and one for 32 mm bulkheads (40mm).
Just get the area wet, start off at an angle to get the bit to bite and apply almost no pressure and let the bit cut. Takes about 5 minutes in 6mm glass.
I am making a couple of tanks and drilling them over christmas so will put up a step by step guide on how to drill some time then.
/www.melevsreef.com/
Fortunately it was right at the start and didn't do any damage.
