OK... bit of work this evening... lots of pics. Lots of mess!
Mocked up the plumbing for the overflow:
Started figuring out the plumbing for where the overflow drains into the sump:
This is with the lid flipped up. The two drains will have 100micron filter bags on them, flip the lid up for filter maintenance:
First divider sitting in place. It obviously needs some epoxy, etc. But this is where it'll sit:
My return to the tank. It's a bit complicated... there will be a hose connected to that dangling barb. The thick part right after the barb is a check valve. The U-turn with the T in it will feed the upper tank return. This return will be a 1/2" or so hole that sprays onto the water surface and does some surface agitation. This hole will also help break the siphon in a power failure, so I'm not relying on the check valve 100% to keep my tank from completely draining into the sump:
Playing with my dual pumps plumbed together; I think I'll need a couple more check valves here... I realised today that if one pump quits, the other pump will just pump through the dead one and back into the sump... so instead of a redundant system, I have a system that's twice as likely to fail!
Put a coat of Varathane on the front of the tank. Shiny! After I'm done finishing the front of the tank I'll mask it pretty thoroughly, because I'm sick of cleaning it and fretting about scratches.
Mocked another divider into the sump, and put a drawer full of bio-balls in there, to get a feel for how much media I have (2 drawers full) and how much space it'll need in the sump. I cut the second divider that'll wall in the trickle chamber, too:
I was wondering why my garage floor was so wet from my relatively short sump experiments... when I realised the stupid bin I'd been using to submerge the pumps in had a hole in it:
And lastly, a sketch of my sump design: