Haven't had any problems drilling a ten gallon tanks. Would suspect the thickness is similar on a tank as small as yours. I used a dremel with a bit made for ceramic tile. Could pull out the exact model number if you want. It wasn't just a drill bit, but had teeth running up the shank about and inch from the tip. Look for the ceramic tile bit. Punched it all the way through...gently (and it didn't take much).....and then brought it around fill circle. I'd drawn the circle on the glass. Also had a hose of running water washing over it as I cut. First time was simpler than I'd expected. Don't need to worry about it being perfectly round.....the bulkhead overlaps the hole by a decent bit. I'd use 1/2 inch bulkheads.
tom
