[Erik]

I wouldn't use any kind of commercial cleanser (Comet/Ajax etc). The stuff will get into the seams around the lenses and will stay there for a long time, and you will get that crap in your eyes and nose... unpleasant! Toothpaste taste and smell is not irritating.
Once the mask is truly cleaned, then monitor to see if you're breathing into and out of the mask a lot- if you are, that will fog the mask no matter how much spit you put in there.
Cheers,
Erik