Guys, even if you're WRONG about it, you can't get sued for slander for calling the police and saying "I'm at a hotel and I smell marijuana in the hallway."

The cops may or may not come.
If the cops come, they may or may not actually attempt to find the source of the pot.
If the cops find the source of the pot, they may or may not actually arrest anybody.

But there's no "slander" case no matter what happens. One scenario: cops come, find nothing, and leave. As long as they don't have reason to believe that you were pranking them, that is the end of it.