It sort of depends on how you define FOD. It's very difficult to go into a fuel tank that has held fuel, and not leave any residue behind.
When we were doing the 747-8 flight testing, they needed to go into the number 3 tank of one of the flight test aircraft for some reason. A few flights later, we got an impending bypass on the #3 engine fuel filter. After the filter was removed and inspected, it was discovered that filter was filled with fibers from the protective garments that were used when entering the fuel tank.