I am very much afraid when water started circulating, the plug would be swept along until it came to a tight spot and block the flow. You have to get it out, and I doubt that it will be easy. Chances are it is in a hard place to work. Likely it didn't go very far. I think you need to somehow get a mirror, or even a shard of a broken one in where you can see where it is and try to fish it out with a piece of wire or even one of those grabber tools. I am glad I am advising, rather than having to do the job. I have a light bulb with wires soldered to the contacts and clamps to the battery. It is great for lighting up difficult areas. Good luck.