I realize this has probably been posted already but nevertheless:

Where: On Rust coming out of the spawn that is at the very end of the pipe line and is by the C point in Domination there is a rusty square section in the wall to your left headed towards the far end of the pipe

What it does: you can throw nades, rockets, etc. out of it.

one very interesting thing happens when you throw a care package marker out of it
when the care package lands it will teleport inside of the map right next to the soft spot

One thing is, I'm not sure if it does this every time as I personally don't use care packages very often
so use this at your own risk it's not my fault your EMP/Chopper/AC130 got stuck out of the map because you did this