I agree with John on this one. I use CLR full strength. I did this yesterday to both my washers, I put the stuff in without water in the unit, fill up with 80degree water , let stand for one hour, then drain though the bottom, then wash for another two hours, Here in Toronto I find that I have to clean these units 2-4 times a year.
I have not tried bleach ,but have done so on regular trays and it works, so I cannot think why regular bleach wouln't work as well