dont drill the holes in the back, whoever told you to do that to a reef ready tank needs to be slapped in the ear.
the two large holes are drains, the smaller holes are returns, its done deal, they are made like this for simplicity and keeping the plumbing together. IMO
outside plumbing looks like crap on a tank such as these.
Just get a set of durso's for the drains and it will be quiet. But do not drill the glass, that would be a big waste of money.