Plot: Landscaping contractor Roger Cook visits Harvard University to learn about their new organic lawn-care program and shows host Kevin O'Connor how to make his own "compost tea. " Then, Roger and Kevin, along with general contractor Tom Silva and plumbing and heating expert Richard Trethewey ask, "What is it?" Afterward, Tom helps a homeowner prevent mildew in his attic by re-routing a bathroom fan that was improperly vented near a soffit