SeeSaw, if I were you I'd drain the hydraulic cylinder before using it. Take off both hoses, hang them to drain, it will take a while. Then drain out what will run out of the cylinder, and then moving the piston back and forth to get out the rest, from each port. Caution, when you move the piston the fluid will spurt out, because the piston will stick and then jump an inch.
By doing this you will keep a bunch of crud, possibly water, and certainly unknown condition and brand of fluid from mixing with your tractor's fluid.
Now would be a great time to put on all new hoses if there is any visible damage on the old ones. And take the time to tape them together and make them the right length for your setup, strain relieve them, etc.