drilled bio cube?

Is the question whether or not it can be done? Or are you asking for help to do it? I know it can and has been done, but I do believe the bottom is tempered.

 

i drilled the back of mine a few years ago, but as stated i wouldn't try drilling the bottm of anything.

 

i drilled mine in the last chamber about 4 inches from the top or so. i had to cut my bulkhead down to get it to fit but it worked really well.

 

So long as you drill it anyplace that the overflow covers on the back or bottom, you are safe. The reason people like to do the bottom is because it makes for a flush line-up (nothing "poking" out the back) and less plumbing is needed to get the water from the tank to the sump.