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.