When introducing a vacuum, don't tie the horse but rather hold onto the lead shank. It is a big mental shift for the horse and the hose takes on less significance. Show the horse the wand and hose from in front so he can see it with both eyes. Too often we just approach the neck or shoulder and get a bit of a reaction. This is because the horse is seeing it with one eye and his vision for things behind his head is poorer than when in front. That is why when alarmed a horse will turn right around to face it, head up trying to better see what it is.