I have 3 toilets in the house all of which have a black deposit in the tank. The material accumulates on the right bottom of all the toilets for whatever reason.
It's consistency is similar to graphite lubricant. It causes black streaks in the bowl which are difficult to clean out.

I have a water softener. I do not have a water filter of any type.

A few posts I have found say this might be due to a breakdown of the rubber in the tank. I have lived in the house for 34 years and this is a recent issue - in the last 2-3 years.

Any ideas?

As your research indicated, the most common cause of your symptoms is breakdown of the black rubber hose inside the stainless steel supply line. You could turn off the supply valve, remove one line to inspect it, then replace them all with matching hoses. If you are not comfortable with this task, call a plumber!

There is NO, repeat NO, stainless steel supply line.

There IS a 'braided' stainless steel mesh OVER the crap supply tube (purportedly to prevent a 'blow-out').

Said blow-out protection would not be necessary if a solid connection were used.






or, if you MUST use plastic: [www.brasscraft.com]


[www.plumbingsupply.com]

Why is this not a general problem? Others I have talked to don't have this issue. What causes the breakdown?

Also, note that one of these hoses is just a few months old. Does this tell you anything?

different hoses have different compositions

'some' municipalities use chloramine some do not

>Why is this not a general problem? Others I have talked to don't have this issue. What causes the breakdown?

It is indeed a "general" problem. 100% of hoses fail in time. Did you ask the others the exact age and composition of their braided lines, along with their water composition as mentioned by Bern?