RE: Can't Purge engine
If you don't prefer the taste of nitro exhaust, you can use a utility syringe to push air into the exhaust line.
[link=http://www.allelectronics.com/cgi-bin/item/SYR-1/780/20_CC_PLASTIC_SYRINGE_.html]LINK[/link]
I also use syringes then this for adding exact amounts of oil to my shocks.