As far as I know, most (not all, I'm sure) tanks under 55 gal
do not use tempered glass. The ones that do typically only have it on the bottom. What I'm basing this on is the new tanks that come into the store. If they have tempered glass, they are marked. I'm assuming that the ones that are not marked are not tempered. Nejsux submitted an excellent post on tempered glass and why you can't drill it. I'm using a 10g as a sump under a 20g and it seems adequate. I agree with Mark that a 10 is on the small side for a 40. Mine is very crowded with 2 heaters, a small skimmer, and a submersible return pump. I doubly agree with losing the wet/dry media and using the LR
for bio filtration (wet/dry=nitrate). I also had trouble with micro bubbles coming from the skimmer return. I solved it by sitting a plastic water glass under the skimmer return. By the time the water flows out of the glass, the bubbles have dissipated...crazy I know, but it worked. IMO
, a Rubbermaid tub would work well. If you want to use a glass tank, probably a 20 long would be better. Maybe that 10 could become a quarantine tank?
If you decide to use the 10, I can post some pics of mine if you wish...might be good for an idea or two. Unless you have access to a good (well adjusted that will make perfectly square cuts) table saw, I'd buy an overflow. Also, don't silicone acrylic together...it tends, as Mark said, not to stick well.