Roger shows homeowner Doug Ferguson of Hudson, Massachusetts how to recycle his yard waste through composting. They visit a compost bin test site where they meet compost expert Ann McGovern from the Massachusetts Department of Environmental Protection. Then Roger, Tom, Richard and Kevin ask, "What Is It?" in the Ask This Old House loft. Later, Richard helps homeowner Kate Smukler of Arlington, Massachusetts remove an old cast-iron house trap on her main sewer line so that a clog can be easily cleared.