I'm sitting at the PC and there is a really bad smell coming from the ssink - like that bad drain smell that you can get. When I went to investigate the plughole was full of bubbles from the washing machine, which had come up the plug hole instead of down the pipe and the most awful smell coming up it.
We had problems a while ago with water from the sink going in the inlet pipe and sitting in the drum of the washing machine. Oh yuk, its horrible