When someone likes a certain sump but wants it bigger, what happens is a new model is born. The Model F layout was what the customer wanted, but they wanted it BIGGER. The layout is the same, although there's a larger bubble tower in this particular sump so the user could place carbon in that compartment whenever he desired.
This sump is very similar to the original Model F, but has been modified slightly to include a large intake chamber.
This is the intake section. The water enters the rear right corner. This chamber can be filled up with LR rubble, to break up the bubbles. Water will flow out the teeth at the base. Visible to the right is a probe-holding bracket for pH, temperature, and ORP probes. A small stand was created to lift the skimmer up to the proper water level for peak efficiency.
The new owner wanted a large refugium, which is on the right in the above image. Water will enter this sump from both ends via two separate drain lines. The water then flows to the center section, which is the return zone.
This sump is quite large, being that it is 54" long x 15" wide x 18" tall. It holds almost 60 gallons to the top.
Skimmer section - 15" x 14.5" x 9"
Extra volume can hold 25 gallons
The intake chamber could also be used to run carbon perhaps. It would need to be in a micro-mesh bag supported by some egg-crate.