Order of the Phoenix Ch. 23:

“And Dumbledore — what about Molly?” said Professor McGonagall, pausing at the door. “That will be a job for Fawkes when he has finished keeping a lookout for anybody approaching,” said Dumbledore. “But she may already know . . . that excellent clock of hers . . .” Harry knew Dumbledore was referring to the clock that told, not the time, but the whereabouts and conditions of the various Weasley family members, and with a pang he thought that Mr. Weasley’s hand must, even now, be pointing at “mortal peril.”

How did Dumbledore know about the clock?

Was Dumbledore ever at the Weasley's house?