No, one cigarette butt would not cause that problem. 100 cigarette butts would not have caused that problem. You just happened to notice your problem at the same time your friend happened to throw a butt in the toilet.

Your problem is related to the fresh water input or, the parts in the toilet tank deteriorating. Is this a toilet that doesn't get used much? Are you on a well system? If you have other toilets in the house, check the tank in them also to see if the gunk is floating in there too.

Hi one cigarette but will cause nothing and the land lord will laugh about it but it is great to be concerned. Most toilet tanks are like that after while nothing to worry about it could be caused by minerals and things like that.

Okay, toilet 101: Only fresh water enters the toilet tank (the part that sits on top in the back). When you flush the toilet, water flows from the tank into the bowl (the base, the part you sit on, where the waste matter goes) by gravity and from the bowl into the toilet drain line and down to your septic tank. There is NO WAY for anything from the bowl to flow to the tank. It is not physically possible, unless your toilet is installed upside down on the ceiling, but I'm certain you would have noticed that.

The reason you have black stuff is that a toilet tank is mostly stagnant water, making it fairly easy for mold or bacteria to grow in it. Since you are on a septic system, you should not use bleach tablets, but you can turn off the toilet supply valve, flush the toilet until the tank is fairly empty and then scrub it. You can even spray it with a mild bleach solution (a one-time application will not harm your septic system). Then open the toilet supply valve and go back to using your gunk-free toilet.