Plumbing--need your help

[Delphinus]

The blue lines are your overflow lines? Ok, it's not going to work (sorry). You need to add an overflow box over the holes.

Problem #1 - in a power failure, water will drain to the lowest point - the lower of the two holes. That's a lot of water volume draining into your sump - unless your sump has enough "empty capacity" it will spill onto your floor.

Problem #2 - you'll never get water level control in the main tank. Ie., you'll likely only get a couple inches at best of water pushing above the holes. You probably want water up near the top of the tank.

My suggestion - get some glass pieces cut and silicone them in over the holes to make internal overflow boxes. Here's what I mean (this is the tank journal thread of my 65G FW tank, it shows the overflow box idea that I'm suggesting might work well for you. The glass cost was minimal - something like $15 IIRC):
http://www.canreef.com/vbulletin/showthread.php?t=28505