The union that connects the copper pipe and the nipple that comes out of the
heater for the hot water is corroded. I got a plumber here to replace it.
He got here, turned off water, turned off electric, unscrewed the union and
wow, I saw some scary stuff. Inside the union. It's black, looks like a
pile of tar. I could not believe it. I was wondering if it could be sewage
back flowing into the water heater, totally black yucky stuff. He looked at
it and told me it's normal, just "stuff" from minerals in the water getting
heated and turn into this. Is this normal? It looks scary to me, that
stuff is in the water I take shower with? Could it be sewage blackflow?

MC