Need advice on overflow

[sbin]

Looking for a used +250 systems and found a deal on a complete setup with lights,fish,chiller,coral,tank,stand for the price of live rock in the tank.Unfortunately the tank is not drilled and uses large canister filters I need advice on how to connect a large tank that has not been drilled to a sump/refug/frag setup.
I have water feed diamond tools for granite work and a friend with a commercial glass shop but that doesn''t help with tempered glass.
Any and all suggestions would be most appreciated.We have a thriving 125g RR tank and want to expand.I am fortunate to have a wife that is as interested in the hoby as I am.

 

[Ed Reef]

Hmmmmm this tank sound like it was build for FW?? If it's so, best to check on the thickness of the glass before you go any further

 

[Kreeger1]

what did you find

 

[sbin]

Found a 84x24x30 265g setup that has been running for about two years with 500 pounds of live rock, chiller, uv, lights,ro system,,high end canister filters ,fish and coral.If the tank was drilled or RR I would have bought it already but it isn't.We want to connect the tank to a refuge/sump/frag setup that will be located in a room directly behind the tank.
The only options I can think of are drilling the tank or pumping the water twice in/out.Any advice/parctical would be most welcome