Temp. of glass before drilling

I don't think it really matters, but it's going to be more comfortable for you inside.

I remember the first time I drilled a tank.  I was scared to death that I would crack the tank and ruin it.  Since that first one, I have drilled probably about 50 holes in tanks and have never had a problem.  I have done the cold, hot, lots of water over the drill site, and not so much water flowing over the drill site.  The one thing I do reccomend, and if I was up North would be glad to let any of you borrow it, is a device that goes on to a handheld power drill that turns it into a Drill Press.  I bought it at Sears about two years ago.  It has rubber feet, and two bars that act as guides.  It is very stable, and does not allow any lateral movement as you drill..  I think the thing cost me about 25 bucks at Sears...