Heck, I am a little baffled by your question. I don’t understand why anyone would need advice on where to put a plunger. Unless the toilet area is so tiny that it wouldn’t fit, why would anyone put a plunger anywhere but right next to the toilet (next to the tank). And, not knowing the layout of your bathroom, how can anyone give you advice on where to put it? When there is an emergency, you need to be able to grab it and use it. Why in the world would you make your guest ask you where the plunger is? As a guest I would be embarrassed if I had to ask for a plunger, and irritated if I had to text the host and wait around for an answer!
Also, I would never put a used one in a rental. A nice clean new one is mandatory in my opinion. And (if people are worried about the “ick” factor) if it is stored anywhere but right next to the toilet, the person using it will have to carry it back to wherever it is stored (carrying and possibly dripping germs along the way). When the bathroom is cleaned and sanitized after every guest, the plunger should be part of that cleaning.
Ummm, see “Jaquo’s” comments near the top of this post (a moderator): “For the sake of the comfort and peace of mind of your guests, have a plunger somewhere nearby. Even if it’s used only once in ten years.”