Some tips for real trees:
When you first set it up, if it's been in the cold and hasn't completely opened up (if it's been bundled), for the first fill, use warm water. This will help the tree open up. Also, it will be very thirsty for the first couple of days so be sure to keep an eye on the water level.
As for getting the water in, I would think using some sort of funnel would work but as someone else said, you have to have some way of watching the level.
You may also want to get one of those big tree garbage bags. Set it down first and then put the tree stand in it before you put your tree up. This will make it much easier to remove the tree from the house without getting needles all over the place.