its easy to drill...... except that damn tempered glass! thin tanks like 10g are a pain to drill since the glass is so brittle, they break really easily during and afterwards.
i have bits and a drill too =)
theres plenty of how tos floating around about how to do it and the pitfalls.
generally people only drill the backs of tanks since bottoms are often tempered. i know if you have an AGA their website has info on which tanks have tempered bottoms, i think its midsize and up basically.
PhoenixOne, a closed loop system is like.... having 2 holes in your tank attached to a circulating external pump, one hole for intake the other for output; although you could have multiple for each, its even recommended in case one gets blocked. its another method of introducing flow in your tank. there are devices that can randomize the flow when you have multiple inputs. personally i dont like them, im too afraid of floods. i'd rather have oscillating, wave maker'ed powerheads and surge devices.