Still have black crystals floating around in toilet

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?
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Take a sample to the city water dept. or call them to come to your house to analyze the water.
Frank

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Thanks Frank- I didn't think of that. I will call the city and tell them about the problem. . Frank K. wrote:

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snipped-for-privacy@hotmail.com wrote:

Sure. Could be coming upstream from some supply pipe repair or the water company flushing the system, or some idiot homeowner that is allowing stuff to siphon into the system.
The question is what are they "little black rocks?" How big? less than 1/16" 1/16"-1/8", etc. Soft or hard? Do they crush into a powder? Your best bet is to contact your water company and ask.
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Perhaps you did not seem my original post on this.
Yes, it can be from the city water. Yes, they are easily stopped with a filter in the line.
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