Hi Golfnut, I have exactly the same experience, and I too have been told that it is bile and simply the digestive juices when there's no food for it to 'mix' with. Sounds like we have the same amount too, it doesn't worry me really but I do try to eat once I wake up rather than leave it til later to avoid more fluid/juices coming through. I do anything to avoid getting dehydrated!!
Oh and don't eat too much at night cos I think it will stimulate the stoma to work more!