Here's mine. 240g dt and 2x 100g rubbermaid. 3" waste pipe hard plumbed into two external overflows. All with unions. Sumps connected by two 2" pvc through 4 uniseals. Etss 1400 and Etss 800 skimmers. Refugium, Biopellets, chiller, ATO, Heaters. Hammerhead running chiller, overflows in dt and Etss 800.
The etss 800 isn't in the picture, but it's sitting on a platform between the two sumps.
Got my sump as organized as it will get so I snapped a pic and found this old thread. Pet food dispenser under a 18 gallon nano reef. In the sump there is a heater, a Remora skimmer converted for in sump use, a float valve connected to the RO/DI water supply, the return pump, and a temp sensor. Also in the cabinet there is an apex Jr with a pm1 module and a DIY breakout box (mounted on the door), and a wireless adapter. I hang a bag of GFO in the outlet stream of the skimmer. There are also leak detectors and a power failure detector wired into the breakout box. Pretty basic. Just like the tank, a lot of stuff in a little space. It's pretty well complete at this point with my only short term upgrade plan to replace the single oversized 250w heater (we keep the house very cold in winter) with two 100w heaters for reliability improvement. I have a UPS on order for the Apex but that's not really a sump cabinet thing.