I started doing this with my roux a few years back, it's a good trick that makes a better pot of gumbo. Lay out a thick bed of paper towels as you would to drain anything of oil, but a lot thicker. When you get your roux to the color you want, slowly pour it out onto the towels and let all the oil drain out of it. After about an hour the roux gets a firmer texture to it, and you can scoop off some and add it to a boiling stock. This way you add and taste until you get the right flavor instead of just dumping it all with the oil in the pot. It also keeps the gumbo much lighter and not greasy. Also the rest freezes nicely, doesn't really freeze just firms up. I usually make enough for a couple pots of gumbo so I don't have to make it every time.