Alex Graham was a fixture behind the wheel of Engine 21, part of a crew known as the Alley Rats that raced to calls around Northwest Washington’s Adams Morgan neighborhood. But it was in Graham’s less flashy work on the training grounds at the other end of the city where the 48-year-old became the department’s go-to fix-it man, making sure water flowed from engines and through hoses at the required rate and that ladders could be raised to burning structures. The 17-year veteran known as “Big Al” suffered a heart attack and collapsed on Thursday while conducting a water flow test at the training facility in Blue Plains and died Sunday surrounded by his family at George Washington University Hospital, a department spokesman said. He is the District’s 101st firefighter to die in the line of duty and the first since Lt. Kevin McRae had a heart attack at a fire in Shaw in 2015.