Did you transfer it into a gallon jug? That's what I do, then I place it in the fridge so the yeast can flocculate and decant as much of the trub (and beer) as possible. I use my yeast cake by the next day, usually. I just plan my brews so that when one is done fermenting I make another and repitch, this way the yeast stays relatively fresh. I believe when the yeast is properly stored it can remain for up to a month or more. Just be careful if you bottle it, make sure fermentation is complete, because you don't want bottle bombs. I think the best solution is to use it as soon as you can, that way it's fresh and viable.