I agree there's currently not much to choose from for your nano tank in regards to protein skimmers . The fission is the only model that fits in you sump. It's important to me to keep the original attractive look of the JBJ nano tank and not have to have exessive electrical wires, filter tubes, and hang on filters outside of the tank.
I think the drain tube is actually the air intake for the skimmer. Anyway's it does a good job of skimming my 24, even though its delicate. I've had it setup about a day and my coral already looks better. I checked PH and there has been no drop in 24 hours. My tank's PH has been a steady 8.0 for a long time, but I will test it every day for a few days. Also, the skimmer's collection tank is not filling as quickly as it did the first 24 hours, which is a good thing. I think it captured a lot of protein the first day it was on.