My 125 gallon tank set up

[LoneStar]

I would keep each drain seperate running into the sump. It would be more as a redundancy that anything else.

Caferacermike pretty much answered who Dan was here:
http://www.maast.org/forums/showthread.php?t=46466

Some of the older members here know Dan but he is pretty hard to get ahold of.

[Gilbert]

you should try and get both overflows going to the bioballs, that would be the best solution to make sure waste gets out of the tank. and the overflows should have 2 bulkheads each, one hole is to move the water in the sump and the other is for the return. as far as the chambers, you can do what ever you want with them, i have seen peoples tanks with just bioballs, just a fuge, with both, and some have removed the bioballs and just used rumble. but the smaller chambers usually are for chemicals or those filter sponge things.

[fishforlife]

Would this be a better set up? Both overflows going into the Bioballs and the return back to the tank.

[FossilReef]

I would stick to both overflows going into the sump independently, easier to solve a problem that way. Also, I would ditch the bioballs and put rubble in that compartment. I've seen too many tanks that had problems with nitrates because of all of the funk that gets caught in/grows on those things. As to the small chamber with the "X" you could put a clump of Chaetomorpha in there and light that section of the sump with a small t5 household light to make a refugium. The way that sump is built, a clump of chaeto should keep rotating enough to maximize growth and therefore suck as many nutrients out of the water as possible. If you plan on keeping herbivores like tangs or angels you could just as easily use Gracilaria and give some to them for a treat every now and then. Just my thoughts on the subject.
Happy reefing,
Jason