I did roast beef in the slow cooker yesterday. Not sure what brisket is but I did mine by rolling it in pepper, salt and herbs and then browning well all over. I chopped some carrots, leeks and onions in large chunks and lay them on the bottom of the slow cooker and rested the browned beef on top.
I didn't add any liquid at all.
I put it on high for around 5 hours. It was really tasty and very tender but it was difficult to slice so I just broke it into chunks.