He appears in "The One Where Ross Is Fine" where he and Colleen kindly invite Monica and Chandler to their apartment to talk about adopting. When Chandler goes to use the bathroom, he bumps into Owen and tells him he's adopted, to which the boy freaks out (because he didn't know yet). Monica and Chandler try to leave while Bill and Colleen are in the kitchen getting snacks and return before the married couple can escape. When Colleen says they didn't tell him he's adopted, Chandler says that kids are so intuitive with Owen coming into the room and cries "I'm adopted?!". Bill asks where he heard it which results in Owen saying Chandler told him he's adopted which results in a small argument.
Throughout the rest of Season 10, Bill is never seen or mentioned again.