External Leaking

On the airplane, there was a sign posted in the bathroom.  The words read something like this:

Please do not put objects other than toilet paper into the toilet.  This may cause external leaking and poses a health risk to the general public.

I wasn't about to throw something into the toilet, but this somewhat subjective rule made me nervous.  What if I accidentally dropped a typewriter into the toilet? Or a hedge trimmer?  

Regardless of the objects that I might accidentally drop in there, I couldn't help but imagine the embarrassment I would experience when I left the bathroom.  External leaking does not sound like something I could hide.