Thanks puckbs. You're right ... it took a bit to find on AGA's site, but found it... only mentions the bottoms being tempered or not ... and neither 20 gallon options are. So, it sounds as though the sides (especially on smaller tanks) generally are not tempered, just the bottoms? I'm looking to use as part of a sump set up, so looking to drill the upper part of a side for a bulk head to drain in to a secondary sump before pumping back to the display tank. I think I'm going to give drilling this a shot in the next day or so and see what happens (need to pick up a bit first) ... thanks for the replies!!