Plumbing Help

I need some help with plumbing on my 265 gallon aquarium. I decided that after a year of having my system up and running to tear it down. I like most newbie made classic mistakes and my tank was overrun with algae, unwanted critters, etc. My question on plumbing is with the drain line specifically. I'm not an artist but here is what I am trying to do.

The top Picture is of the stand setup for a reef ready tank with dual corner overflow. Each side has a 1.5" drain which converts below into a 1" line. The returns are 1". On the bottom picture I want to change the return to another 1.5 drain. Has anyone done this? I ran a durso overflow originally. Has anyone done two dursos in a stock tank? I decided to run my return lines externally up the back of the tank but I'm not running the typical 1" pipe. I've change this to a 1.5" pipe which will T off and run to each side of the tank with two penductors on each end. The pump driving the return will be the same a Reeflo Snapper/Dart Hybrid running the Dart impeller at 3600gph. So with the increase diameter in return pipe, does anyone think that the single 1.5' drain on each side work? Has anyone done this before? here are some pics of the return plumbing I'm working on.

 

Re-drilling a hole is going to be tough. I'd think you'd need a drill press or a very stable jig to do so. Do you have powerhead's that will be used for water movement, or is your return the only flow? You don't need 3600 GPH running through your sump. It will hinder your filtration. The two 1.5" drains should be fine, just match a pump to the flow.

EDIT: Nice Hog!

 

FOD. My son loves his HOG. I was running the dart with just the two 1.5 overflows before I broke it down. The flow was good but ran a little on the high side about an inch of water line before the top. I'm running two MP40's in the tank. What do you suggest I do with the exist 1" return line. Should I use it as an emergency drain in case of a blockage?

 

Here is a chart for PVC that might help. Also, the actual overflow box itself will be limited. Are you trying to accomplish extra flow?? I would advise against 3600 gph through a sump.
My vote for YOU would be add powerheads...

But I like to mod and build... Me personally... I would leave the overflows/returns alone. I would drill into the back panel of the tank and do a closed loop system with a SCWD or a Motions Ocean. The sides of the tank SHOULDN'T be hardened glass.