"Show me your Biocube mods"

[Enigma]

I'm not sure how the chambers are set up on the Biocubes, but if I were to drill a Nano Cube, it would definitely be the centre chamber that I drilled. I would still use a media basket in the first chamber for filter floss, Purigen, and charcoal. I would want all of the water to pass through that into the second chamber, where it would then flow into the sump. I would have the return from the sump entering the return chamber, though I know some people have that coming into the centre chamber, too.

10-20 gallons isn't a big sump, and there is only so much that you're going to be able to squeeze into it (especially if you're going to build a fuge in it). Continuing to utilize the first chamber for some filtration is going to help save space in the sump: for things that absolutely need to go into the sump.