I disagree with the statement . I have three Tanks and three Canister Filters . One a 40 is all that I use . My 100 I use one to add Media, and have a sump. My Third which started as a stand alone 55 , upgraded to a 75 I was going to run 2 Canister filters , as it was a fresh water set up from years ago. Lately I too drilled my Tank . I tried myself . Not for the uneducated or inexperienced , I screwed up the second hole , and the Tank was compromised. I took it apart , bought another 75 the same . I had a local Glass and mirror guy cut up the ruined tank for the sump baffles as glass that thickness is huge money to me. The old Tank glass was 7 mm and to get 5 pieces cut it was around $50 Canadian , The Holes cost $ 26. and I had great advice from a member all the way through. He shall remain nameless until it is all set up and running . If you are planning on drilling it yourself , and want the best guidance going I will ask if its ok with Him to Connect you. i was inspired to go Canister alone by the above Gentleman Mr. Mojo Rising. The only reason for adding a Sump which I am making myself from a 40 breeder is because I don't like the looks of HOB Skimmers , plus the danger of it overflowing.
All that just to Advise you of my overflow choice . It is a Modular Marine , check out their website . They are beautifully made . They will drill the drain holes as you wish , but I went with a Bean Animal 3 pipe . It is a what they call a low profile . The thing about the design is that they will not overflow as the wier , and box are at the same level. It has been very educational . I just siliconed in my first " dam " baffle this morning . I stink at doing silicone but following advice it turned out really well. Just another approach to think about . A lot of work and extra money to have an Internal Skimmer . I still have to pipe the Sump and buy a pump to return the water to the display .