Hi van637. Yes there is a way you can have a sump without drilling. You'll need to either buy an overflow box to drain water down to your sump or make your own overflow. Then you just need a pump in the sump to return water to the main tank. Just make sure the return pump can push more water up then what your overflow system can bring down so your sump doesn't overflow.
I'll look for some pics to help explain. Actually if you just google overflow box you'll be able to see several different types. If you're interested in making your own the following link shows one option.
I actually made one myself and it worked but in the end decided against using it because I didn't like the look of it.
I disagree. You want the overflow to be rated higher than the pump. You also want to ensure that the overflow will not drain the tank below a set level. This ensures that your tank will always be "full" (the level determined by the overflow), and that your tank does not overflow.
Also, this set up ensures that if power is lost your tank will not completely empty into your sump. Just make sure that your return line from your pump has a siphon break.
I would listen to the other guys. I've obviously got my info muddled up. Ken knows way more than me. Plus I never ran my setup on my tank because I didn't like the look of it. I just got a second filter. Sorry if I gave you a bum steer.
As far as an overhead pump, vs the sump pump. what should you be using. In the distant future i want to set up a 75 gallon reef tank. And was wondering what should the overflow be and what should the pump in the sump be?