No. Mini-sump. He wrote it there.
Anyways, you will probably be successful with minisumps if you'd like. You don't even need to drill anything probably if you'd rather have a HOB
It would probably be a good idea to go the sump way instead of HOB
filters or canisters if you are planning a mini-reef. I've seen successful 20G reef tanks in this forum and they are awesome.
Refugiums are a little too much work for you for a little 20G although I've seen HOB
refugiums in the market with trickle systems within the kit. Most definitely you could have a great time practicing on a 20G mini reef with a mini-sump. It's also very movable in case you move from apartment to apartment a lot.