I cook sous vide all the time. The liquid that you drain out of the bag is not rich and flavorful. It's thin, watery and very greasy. If you've seasoned your meat well before cooking in the water bath, the liquid is also very salty. Once reduced, it's pretty inedible. It does not make a good sauce. If you insist on trying to use it, pour it into a cup and let it sit until it's cool, then remove the fat.
It you want to make a reduction sauce after sous vide, pat the meat dry, then quickly sear it in an extremely hot cast iron skillet with just a little fat. You only want to sear - not cook the meat any further. Then deglaze the pan with some wine or stock (or your leftover liquid) and reduce. If you want to learn about emulsions, off-heat swirl (don't stir) cold butter into your sauce.
Or ..... make mayonnaise. It's the perfect lesson in emulsions.