Hundreds of tons of waste still languish inside a tin-roofed warehouse in a corner of the old grounds of the Union Carbide pesticide factory here, nearly a quarter-century after a poison gas leak killed thousands and turned this ancient city into a notorious symbol of industrial disaster…Advocates…insist that Dow Chemical Company, which bought Union Carbide in 2001, also bought its liabilities and should pay for the cleanup…Dow…says it bears no responsibility to clean up a mess it did not make…