Low temperature washes cause this problem, and about the only thing that you can do is to run a full heat programme from time to time to keep bacteria at bay. Some domestos down the sink plug wont do any harm, but it wont really go where its needed - ie into the drum area itself. Tablets such as Calgon dont clean the inside of your machine, they just help to prevent calcium build up by softening the water.
John
July 2009