With the barrels I used , I just put my pump in the bottom of the barrel, and put lava rock in mesh bags around it, so I didn't need bulkheads or to make holes in the barrel.
When media needed rinsing, I'd just pull out the mesh bags and hose it off.
Ran a PVC line off the outflow of the pump to the tanks. You can see in the photos I suspended filter socks for mechanical filtration.
I have found you can put the barrels in a different room, or even in a basement if your pump has enough head pressure.
I knew a guy who put his sump barrel on a cool basement floor, even though his tank was 1 floor up. It kept his salt water species cooler during summer heat waves.

In the photo above, the bags of bio-media are removed for rinsing, and you can see the pump sitting on the bottom of the barrel, and PVC line heading up vertically toward the tanks.