When hooking up redstone exactly like I did in the video (doesn't matter orientation, but you must go down one block where the redstone goes down one block), the second dispenser fires when you first press the button, but doesn't fire anymore until you take out the bucket and put a new one in, while the first one is powered like usual.
(For some reason I get error messages when trying to attach files so here are the links: https://drive.google.com/open?id=13lG3q08zApJriGLsnvPbuGiQxe7mut15 https://drive.google.com/open?id=1qrViQGNcu-r-wI4u59bCBxkEGO7cF5WV)