Bacteria in the tub caused by a combination of low wash temp & eco friendly detergents. Once a month run a 90C wash (obviusly without clothes) & add a decilitre of chlorine. There are several products availble off the shelf, but chlorine & 90C temp does the trick just as well & much cheaper. Clean out the soap tray regularly (you can also put it in the dishwasher on 50C program if you like). When the washer isn't in use leave the door ajar & the soap tray slightly open.
Mike
October 2009