I thought they were from the flapper and rubber seal too, but i did
change the flapper. The old one wasn't breaking apart. It was just old
and i wanted to replace it. Seems like too may rubber pieces to be from
the seal since that is small and the pieces have been coming into the
toilet for over a week. I will clean out the line though that comes
into the toilet. That might help.
RP wrote:
wrote:

I've replaced the fill valve twice {Fluidmaster 400} because the toilet
won't shut off. I've found out why. I'm seeing small black
rocks{charcoal,rust?} floating around in the toilet. They get under the
rubber seal in the fill valve preventing it from shutting off. It
flushes fine a couple of times and then keeps running. Now my wife did
open up the safety valve on the water heater, which she shouldn't have.
Someone told her it would be a good idea to release pressure once in a
while. Is it possible there are rocks in the heater that are going
through the pipes to the toilet?Seems like this problem started after
she messed with the water heater.If not, what could these rocks be? I'm
at a loss to know where thay are coming from. Frustrated. Thanks for
any responses.

Assuming that you aren't feeding your commode with hot water, those are
probably pieces of your flapper or rubber washers.

Richard Perry