Ok - here is my fantastic tip!

Is the bottom of your kettle or urn dirty, rusty etc from buildup? Or does the water taste metaliic? Simply put some water in with a good dose of white vinegar (like 400ml or so to get it really clean) and put it on to boil (i took the lid off so it would boil for longer!). It magically goes shiny and clean. Then just rinse it out