Tapping has alot to do with it also, Always be aware of the health of the tree above and below the tap and as mentioned before do not tap to close to a old tap hole. Some old tap holes are hard to find, but if you look at the tree carefully you can see where a tap hole 15 years old is in a tree by the change in what I call the texture of the bark. I know a lot of sugarmakers just worry about how many holes they can drill in a tree per day and not worry about placement. In the end that will cut down on there quality and quantity. I was watching our local tv news the other night and they had a picture of a bucket on tree that was less then 2 inches from a huge scar, where the bark was missing just over it and it wasn't running, go figure