I recently read something that said one should not wash molds--even
professional rigid plastic molds--with soap, but simply buff the cavities
with a cloth between uses. It suggested using hot water only if any washing
was required.

Is there anyone else here who uses professional plastic molds--I'm not
talking about metal molds--and, if so, do you wash them with soap, in the
dish washer, with hot water only, or what?