cheapo thick bleach. Pour about a fifth of the bottle (bottle not gallon or half gallon container) around the door seal and rub it round with a piece of kitchen paper. You should probably wear gloves to do this bit. Pour the rest of half the bottle in the soap compartment and then run the machine with no clothes in it on the hottest longest setting. Wash something like dusters in the next wash so that if you get the smell of bleach in them it doesn't matter.