"They say" (who is they?) due to the velocity of the water
   during a flush along with the relatively non-stick properties of
   the ceramic, toilet water after a flush might be even cleaner
   than a dog's mouth.

   Yeah. Please don't believe a word of the above. I just made it
   up. I am They. :P* It's what I would've said if I had a kid
   under my care that suddenly got hit by toilet water gun, a
   little OCD and was freaking out about the idea.

   I'd also say it to an adult who suddenly got hit by toilet
   water, a little OCD and was freaking out about the idea.

   I'd also add, "But a dog's mouth _really_ isn't all that clean
   either. Maybe you should clean up".