I have a VERY LARGE home with a hot water problem. I have a large hot water heater along with an extra 250 Gal storage tank. During normal day to day useage, the hot water is fine. The problem is that if I am gone from home for several days, when I get back and turn on the hot water, I get dirty yellow water for several minutes, then the water is OK again. What is my problem and how can I correct it?