I tossed my clay in a bucket of soapy wash water yesterday and after sitting there all day it did show signs of breaking down.
That said, I have clayed with soapy wash water with outstanding success, just don't let the clay stay submerged for long periods if time.
The clay that sat submerged all day sat on a plastic cover overnight and was dry and back to original condition. While I haven't tried using it again I see no reason why it wouldn't work as usual.