You might also consider putting a gate valve on it instead of a petcock, then plumbing that into your exhaust pipe. No mess.
I've considered putting an electronic solenoid valve on mine so I can just push a button inside the cab while driving to blow down my trap. A long enough run of tubing before the valve, and a short shot at low EGT's shouldn't damage it.
But I only blow my home brew trap down every couple months, so its not really a big deal to do it manually.