Doug Fister has always wanted to know how things worked. As a kid, he built cities out of Lincoln Logs and tinkered with Matchbox cars. Tired of her son dismantling her functioning appliances, Jan Fister let him fiddle with a broken vacuum cleaner. Without the benefit of a manual — to Jan’s great surprise — Fister fixed it. In high school, Fister could take apart the front end of his father’s 1970 Monte Carlo and put it back together without instructions. In the minor leagues, Fister worked construction in the offseasons for extra income. He can afford a builder now, but for fun this winter he remodeled his bathroom. “He’s got a mind that is just always going,” Larry Fister said. “He likes a challenge.” The challenge before Fister, 30, as the Washington Nationals prepare to open official workouts for pitchers and catchers Saturday, is to convince his new team he really is not too good to be true. When the Nationals shipped utility man Steve Lombardozzi, lefty reliever Ian Krol and pitching prospect Robbie Ray to Detroit, they received in return a 6-foot-8 workhorse who throws a sinkerball that plunges as if made of cement. They also got the son of a former Merced, Calif., fire captain and SWAT team member; a playoff competitor who stared down the eventual world champs after taking a line drive off the head; an athlete who played high school hoops and runs 10 miles between starts; and a burgeoning star who behaves like a regular guy. “He’s going to sign something like a five-year, $70 million contract one day,” said Mike Batesole, Fister’s coach at Fresno State. “I’m pretty sure he’s going to have $70 million worth of jeans and T-shirts and a pickup truck with stock rims on it.” Fister is the product, foremost, of generations of firefighters and cops. Fister’s paternal great-great-grandfather was a firefighter in the 1800s, his great-grandfather was a county sheriff in Nevada and his grandfather served in the Air Force. His uncle was on the police force, a sniper first and then a detective. After playing football at Fresno State, Larry Fister worked as a police officer for 12 years, spending part of his career on the SWAT team, knocking down doors on raids. He rose to the rank of captain during 20 years with the Merced Fire Department. Fister would practice shooting alongside his dad and flip pancakes at fundraising breakfasts for the fire department. He watched how the men bonded — if one firefighter needed his roof redone, the entire department spent Saturday at his house. Fister studied to be an elementary school teacher in college, but he figures he would have gone into law enforcement or firefighting if not for baseball.