The magnets are quite brittle. Don't let them fall on to hard surfaces (like concrete) from a height – they may shatter into sharp pieces. Straight copper pipe, at least 30cm long. 15 or 22mm ...

If the magnet does not stick to the pipe, residents are asked to scratch the pipe with a penny or other hard object to see if the scraped area is a copper color or shiny silver. If the color is ...