Rizzoli holds a drawing in her hand while she's going into the building where the suspect might have lived. Once she is in the building, the drawing, which is too big to be folded and put in her pocket, has disappeared.
When the dad (a plumber) is telling the son to re-solder a pipe, he says it will leak under pressure. The pipe he is talking about is a drain pipe, which is not under pressure- something any plumber would know.
Dad asks for a j trap and is handed a p trap fitting. Also, something a plumber would spot.