Homeowners in nine East Bay cities who sell or upgrade their properties starting in March must spend hundreds to thousands of dollars replacing their sewer lines under court orders obtained by the federal Environmental Protection Agency.  The orders are an attempt to stop the dumping of as much as 400 million gallons of partially treated sewage into the Bay each year as the result of overflows during rainy weather.  About 50 million gallons of partially treated sewage ended up in the Bay as recently as Oct. 13, when about 4 inches of rain fell on the East Bay.  Most of that was because of broken residential sewer lines that go from  homes to pipes in the street.  One court order, expected to be signed next month by all nine cities, requires the cities to strengthen existing laws or write new ones that require homeowners to fix or replace their lines when a home is sold or upgraded. It also will require those cities to fix their broken sewer collection systems.Â