When sticking your microphone in a pipe, always check these things: 1) What's in the pipe? 2) What's going to be coming and going in the pipe? 3) Always have a softie or something on it to be safe.
During SFX gathering on top of a skyscraper, there was a nice looking pipe that had some cool echo and a regular beeping that I could hear when I put my mic down there. There was also a funky smell and some water sloshing sounds. When I took my mic out, my dead cat looked like a side of it had been licked like actual cat fur looking licked--matted and wet. Always use a softie!
Mic was unscathed.
It turns out that the machines on the roof near the pipe were sewage treatment/water treatment for the building and that also explained the smell coming from the pipe.