overflow guestion

I want to put an over flow on some of my tanks. I have seen people use overflow boxes with numerous different siphion devices. I also see people simply drill a hole near the top of the tank at the water line and use bulkhead fittings. It seems to me that drilling the tank would eliminate any pesky siphion problems. Is there any other advantages / disadvantages that I need to be aware of. I work for a glass company and drilling holes of any size is not a problem.

Yea, Thats what I was thinking. I am going to be drilling the backs of the aquariums. The tanks set on countertops in a rental house and I can not drill into the counters. I was thinking I should drill my hole at the desired water line. Now I am reading that I should drill below the waterline and build an internal overflow box. Any thoughts? I have already drilled one of my tanks at the intended water line.