It's the Rubber seal at the bottom of your water tank, when you flush the rubber seal raises and the water flashes your toilet. Generally its black but not always.
If you have a copper float ball that will do it
The width of a toilet tank can vary in size. The average width of a toilet tank is about 18 inches.
The septic tank has nothing to do with the mold in the toilet, the mold that you have is a bacterial growth common to toilets, the toilet needs to be cleaned more often or a stronger cleaner needs to be used, the septic tank is a holding tank for gray water.Mold grows anywhere there is humidity and warmer temperatures. More then likely it's not mold, it's probably just algae if it's IN the water. It's natural when you have well water. You don't really need to worry about it as you can just clean it out with just a brush and water a few times a year. You don't want to put any "Tank Cleaner" chemicals in the tank or toilet bowl if you have a septic tank as it could kill the "Good" bacteria in your septic tank and you could have all kinds of problems.The home septic tank is for sewage waste that grey water is also stored in. Grey Water is technically just waste water from your sinks, showers, etc.In an RV you usually have a sewage waste tank separate form a Grey Water tank as you can empty the untreated grey water into most any drain. Where as the sewage waste HAS to be emptied into a regulated sewage waste disposal site.
All I know is that everyone's toilet will mold if they don't clean it enough.
They are called tank bolts.
Toilet tank
Will a American standard toilet tank fit a glacier bay toilet
The tank above your toilet.
seal to stop water from runing into tank located between tank and bowk
because mold is really distict from other things such as black mold. black mold is just plain black with little white patches.... that how i tell it from anything else
How do I find out an answer to a question about toilet repair? I have a crack in my tank and I want to fix it. It is ceramic.