Ah ok found the thread you should have just PM'ed the link too LOL
Agree with iambatman the tube should be under water for it to work proper. Next thing ONLY buy a evry very small airpump I'm talking something like 1-2watts max otherwise it'll be wayyy too much action for this lil 2g tank there. Powerhead on that size tank I'd totally skip.
Here's also some sponges http://www.petsolutions.com/Sponge-Filters+C23.aspx
the one's I use in my 10g's are the Bio foam's cause I'm simply too lazy to built them any more lol so I bought these, love them. Just take the same approach with the corner sponge as you want it, have the tube ~2" under the surface and hook it up.
On a side note what seems to work well as far as filtering the water for ya is building a java moss wall; don't ask me why/how but any tank that I have Java moss wall's in the water is wayyy clearer then others; plus it looks real nice, much better then these posters.
Oh another thought you may also wanna check petsmart, they have what they call "Betta bowl filter" and they're super small flat filters that only have 1 thin pad in it and powered by air as well and maybe 2" by 3" in size. Kinda looks like a mini heating pad but its a filter; just in case you don't wanna DIY after all