Hull FC were behind at Wembley for 71 minutes but fought back to win the match in dramatic fashion.
“We’ve shown this year that we’ve pulled games out of the hat in the last 10, 15, 20 minutes a few times,” Washbrook told Love Rugby League.
“It’s not the first time and it probably won’t be the last.
“It feels outstanding. Obviously it’s been a long time coming for the club at Wembley.
“For me, it’s 11 years I’ve been playing and I’ve finally got my hands on some silverware.”
Washbrook paid credit to hooker Danny Houghton and his match-winning tackle.
“Unreal,” he said.
“There’s no many people who would have done that. Just to be there to make the tackle and then to knock the ball free, it’s outstanding.
“The things that I could have done to him at that point you probably can’t say!”
Washbrook said the Black and Whites can now set their sights on a treble.
“It’s still there,” he said.
“We’ll still take it week by week, that’s the way you do it. That’s the way we’ve done it all year.”