Kevin recaps how the roofers applied new architectural shingles to tie the old house in with the addition. Tom shows Kevin the progress on the new back deck. Kevin finds Richard and plumbing contractor Kevin Bilo fighting to keep the P-trap from the new bathtub on the second floor from interfering with the decorative ceiling of the new kitchen. They use a new German bath waste and overflow kit that allows for the flexibility needed to solve the problem. Kevin and Norm finish up the trim and decking on the new corner deck stair. On ASK THIS OLD HOUSE, Tom and Kevin build a watertight fire pit cover in the barn. Then Richard heads to Missouri to upgrade and vent a bathroom sink. And the guys ask, "What is it?"