Ok....I'll prolly get crap for this....I put mine in the washing machine. I do a complete wipe down on the inside and top with clean wet cloths that get rinsed frequently. The sock goes in with low water level, cold water, regular wash, and second rinse. After it's done it looks brand spanking new. It then goes into a pot of cold water with some Seachem Prime for a good final rinse and then it's done.
I've never found another way to get it that clean. Washing by hand just doesn't do it.
-Gregory