I took the advice of someone on this forum and unscrewed the line at
the bottom of the toilet and flushed out the line into a bucket. I
probably flushed out about 20 gallons of water. With each fill of the
bucket there were black rocks{iron sulfide?} although less as i flushed
out more water.My original problem was the toilet wouldn't stop. I
discovered these rocks were under the rubber seal in the
Fluidmaster,preventing the toiulet from stopping.I have copper lines so
i don't think it could be a corrosion problem. Could these rocks be
coming through the city pipes? If so, how would they be able to keep it
from coming through my lines?