I have done this set up for the past 2 years. it works great. and there is no problem with slime building up inside the barrel. i suppose the blue barrel will not let enough sunlight in so it can grow. what i do is build a platform about 4 feet high and place my barrels on top of that. laying it down of course. then have a valve coming out of the bung on the barrel. i then connect pvc 1/2" pipe to that. this runs down to the water pan. i go to Rural King farm supply and pick up a float type valve that connects to the side of the water pan. the gravity flow is good enough to fill the pan. in fact it will compleatly empty the barrel. the barrel will stay cool in the summer as i have it in the shade. i have 20 or more chickens at any given time and they only use a barrel a month if that much. there is two problems with the set up that i see. first the water pan needs to be cleaned about every week or so and it needs a piece of 2x4 wire around it so the chickens will have to stick there heads through to get a drink. if you don't do this they will set on the edge and make a mess. also it has to be drained in the winter because the pipes will burst. hope this helps