drilling them isn't bad at all, although i'll admit i was pretty nervous doing the first one. i bought the bit from i think its called glass-hole cages, or something similar, and drilled 3 tanks with no problem. i actually drilled my 40l sumps, and added a .5 gph continuous drip line into each tank. water goes from the tank thru overflow into sump and then "overflows" (at the same .5gph rate its dripping in) out the hole i drilled and into the basement floor drain via pvc. water changes a thing of the past, at least in the big tanks.