drilling a half full tank

guys i am thinking alot of the war im having with nitrates could be that the overflow pipe out of the top of my tank isnt "surface skimming" enough.

so im thinking of adding a overflow or weir box.

i could run some sort of siphon into the box and use my existing overflow as emergency, but i would have to make it able to restart automatically.
or i could drill the two holes in the back of the tank and do a half siphon (durso) and a full siphon

what are your thoughts. i really don't want to have to remove everything in the tank to drill.

Tricky situation you've got there.. If it was me i would half or 3/4 drain the tank, drill the back and install a "Glassholes" overflow box. I run one on my current 2.5ft tank and it surface skims great, is almost silent (would be if i had a smaller return pump) and because they are black acrylic they sink in with a painted back wall of a tank.

I would very much recommend them. Here is a picture it pre and post installation. The only parts in the first picture that relate to the overflow box is the box itself, and the bulkhead under it. The Loc-Line is for the return, and the other thing is a valve to stop water flushing back out when the pump goes off. Cannot remember the name for it but Glassholes sell them, which is where everything in that picture came from. The mount is for a filter bag which you can get either through Glassholes or Guppies sell them. Both fit with no issues.



Box is up in the left top corner, almost invisible.



As far as drilling the tank itself goes, i'm not really sure the best way to do it upright while its setup.. and without getting glass shards into the tank. I would maybe float some acrylic underneath where the hole is and let any swarf from drilling simply land on the floating acrylic.. I don't really know what the best way to do that would be.

Edit: I considered both a durso setup, a single hole in the bottom with a bulkhead and a weir box, a side mounted overflow box with a bulkhead and a 90 degree piece like my last tank had.. and the Glassholes ended up being the one i went for. Reasons being is the overflow boxes they make are super nice, whereas the last acrylic one i knocked up in the shed didn't turn out super crash hot.. nor did the weirs i've made in the past.. I don't think i'd ever not use a Glassholes overflow box if i was to ever have another tank beyond this current one.

The setup i have now is super simple, fool proof and is reliable as it'll ever be. The valve is not like the shitty ball valves we have here, it is rated up to 70 psi or something, so it will never leak.. and even if it did you just have to run your sumps return chamber low enough with the tanks return itself high enough to not siphon too much water. Not very complicated i thought.