Taxiing jet engines groaned on the tarmac, their fumes filling the Port of Seattle’s firetruck bays on an early summer day here. Snaking hoses connected tanks and filters in a complex cleanup operation. Over six days, the system flushed a toxic substance from a firetruck as the department became one of the first in the nation to begin to remove firefighting foam concentrates laced with “forever chemicals.” For decades, per- and polyfluoroalkyl chemicals, or PFAS, have been used in foams to put out the highest-intensity petroleum-fueled fires — especially important in saving lives amid catastro…