The plumber (David) cleared a drain by opening a trap and snaking it clear. Not as easy or routine as it sounds. Over a period of a few years we have had at least 5 plumbers try to clear that same bathtub and sink trap in our upstairs bathroom. They have all said they could not open the trap because it would break, was unopenable for some other reason (like it was made of lead), we would have to install new pipe around it. So the plumber David from Baker Elman is a hero to us. We will call them again.