It's very likely the bottom is tempered, in which case you could not drill it at all. Depending on the manufacturer, date of manufacture, etc. the sides also may or may not be tempered. Drilling a tank really isn't that hard if its not tempered, just takes patience, plumbers putty, water, a drill, and a diamond studded/tipped hole saw. I've drilled several smaller tanks with absolutely no problems whatsoever, and actually it was a lot easier than I anticipated. I wouldn't hesitate to drill my own holes in a tank from now on....