I am trying to remove an old bathroom sink fixture, including the stopper and have run into a problem. I have removed everything except the 5 inch piping used for the drain that connects directly to the u-shaped pipe carrying the water out. I can't remove the washer at the top of this pipe, directly touching to the sink basin. When I try top twist it off with a wrench, it just moves the entire pipe around. I can not think of a way to leverage the pipe, so that only the washer moves. Any ideas? Please help?

P.S. This sink fixture was originally installed 20 years ago.

Let's see if I have your question right. You are trying to remove a Lavatory sink from your bath room and you have the water supplies unconnected but you can not remove a small chrome pipe that is about 11/4 inch in diameter and is 5 inches long. When you try to turn the nut holding it in the entire pipe turns.
If this is true here is something for you to try, first thing, down in the sink drain about an inch you may see some holes going out the side of the pipe going through the sink. If you do the put a strong screwdriver into each one of the holes and let the screwdrivers cross in the sink. Now try to turn the nut below, it will also try to turn the screwdrivers, but you should hold the screwdrivers so that they will create a tension on each other and not let the pipe turn and then the nut will unscrew. Now if you have a lever coming out of the pipe below the sink you will have to unscrew the thing out of the thing under the sink called a pop-up assembly. If you run into a problem and the thing will not unscrew out of the pop-up then you may have a different type of drain, if that is so this is what I would try. Try to keep the small chrome ring in the bottom of the sink from turning, you may be able to do this by using a screwdriver and tap on the side of the ring in away that would make it turn counterclockwise. You may have to do this while someone is holding the nut under the sink. If this is what you have the little ring will eventually unscrew from the pop-up assembly and the rest will fall out the bottom.

If non of this helps you maybe you could explain a little about what you have and perhaps I can help.