What is the “very disgusting bodily fluid” in Detroit airport soap dispensers? Cops and officials won't say

Cleanup crews are removing what police and Detroit Metro Airport officials are describing as an "unusual substance" discovered in the soap dispensers in the bathrooms. They aren't saying exactly what it is, other than a "bodily fluid" that is "very disgusting." Spoiler alert: they said it isn't saliva. What could it be?

From Click on Detroit:

The unusual substance isn't being tested because sources said it was pretty apparent what the substance was. They said it was likely a bodily fluid, but it hasn't been confirmed because testing hasn't been done. Officials said it's not believed to be spit.

Why would anybody put something in an airport soap dispenser? Investigators said it's nothing sinister, but someone with ongoing access to the restrooms who has a grudge.