robsam
Well Mr. Copp, I just answered this question in another post. Actually when the water heater tank become old(say 3-4 years), it accumulates some water scales and lime in the tank.I think you should try to clean the tank once. As you said that this dirt is coming only when you start the hot water supply. This is happening because there is dirt in tank. You can also give a try to the connections. Ask your plumber to do this. All the best.
